Explain the "Lanthanoid Contraction" and its effect on the size of 5d series elements.

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Detailed Explanation

🔵 What is Lanthanoid Contraction?

Lanthanoid contraction is the gradual decrease in the atomic and ionic radii of the lanthanoid elements from La to Lu with increasing atomic number.

La → Ce → Pr → ... → Lu
Atomic / ionic size gradually decreases ⬇️

The main reason for this contraction is the poor shielding effect of the 4f electrons. As the atomic number increases, electrons are added to the 4f subshell. These 4f electrons do not shield the outer electrons effectively from the increasing nuclear charge.

⚛️ Why Does Lanthanoid Contraction Occur?

1. Across the lanthanoid series, the atomic number increases.
2. Electrons are progressively added to the 4f subshell.
3. 4f electrons have a poor shielding effect.
4. The effective nuclear charge experienced by the outer electrons therefore increases.
5. The electron cloud is pulled closer to the nucleus.
6. Consequently, atomic and ionic radii gradually decrease.

4f shielding is poor → Effective nuclear charge ↑ → Size ↓

🟢 Effect on the 5d Series

One of the most important consequences of lanthanoid contraction is that the elements of the 5d transition series have atomic and ionic radii very similar to their corresponding elements of the 4d series.

Normally, elements in the 5d series should be considerably larger than the corresponding 4d elements because the 5d elements have an additional principal shell. However, the lanthanoid contraction offsets much of this expected increase in size.

4d ≈ 5d

5d elements are unexpectedly small because of lanthanoid contraction.

📊 Important Examples

4d Element	5d Element	Comparison
Zr	Hf	Nearly same size
Nb	Ta	Nearly same size
Mo	W	Nearly same size
Ru	Os	Nearly same size

The most famous example is the pair Zr and Hf. Their atomic and ionic radii are remarkably similar despite Hf belonging to the 5d series.

⭐ Key Point:

Due to lanthanoid contraction, Zr and Hf have almost identical atomic radii.

📌 Other Consequences of Lanthanoid Contraction

• 5d transition elements have sizes similar to their 4d congeners.
• Zr and Hf show very similar chemical properties.
• Separation of Zr and Hf becomes difficult because of their similar sizes and chemical behaviour.
• The basic strength of lanthanoid hydroxides decreases from La(OH)₃ to Lu(OH)₃.
• The density of 5d transition elements is generally high because their masses increase while their atomic sizes remain relatively small.

✅ Final Answer

Lanthanoid contraction is the gradual decrease in the atomic and ionic radii of lanthanoids from La to Lu due to the poor shielding effect of the 4f electrons. This contraction reduces the expected increase in size of the elements that follow the lanthanoids.

As a result, the elements of the 5d series have atomic and ionic radii very similar to those of the corresponding 4d elements. For example, Zr and Hf have nearly identical atomic radii.

Poor 4f shielding → Lanthanoid contraction → 5d size decreases → 4d and 5d sizes become similar

📝 20 MCQs with Answers

1. Lanthanoid contraction refers to:

A) Increase in atomic size from La to Lu

B) Gradual decrease in atomic and ionic size from La to Lu

C) Decrease in atomic number

D) Increase in nuclear size

✅ Answer

B) Gradual decrease in atomic and ionic size from La to Lu.

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2. Lanthanoid contraction is mainly caused by poor shielding of:

A) 1s electrons

B) 2p electrons

C) 4f electrons

D) 5s electrons

✅ Answer

C) 4f electrons

---

3. Lanthanoid contraction occurs from:

A) La to Lu

B) Lu to La

C) Sc to Zn

D) Hf to Hg

✅ Answer

A) La to Lu

---

4. The shielding ability of 4f electrons is:

A) Very high

B) Poor

C) Perfect

D) Zero nuclear charge

✅ Answer

B) Poor

---

5. Due to lanthanoid contraction, effective nuclear charge:

A) Decreases

B) Increases

C) Remains zero

D) Becomes negative

✅ Answer

B) Increases

---

6. Which pair has nearly similar atomic radii because of lanthanoid contraction?

A) Na and K

B) Li and Na

C) Zr and Hf

D) Cl and Br

✅ Answer

C) Zr and Hf

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7. Hf belongs to which series?

A) 3d

B) 4d

C) 5d

D) 6d

✅ Answer

C) 5d

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8. Zr belongs to which transition series?

A) 3d

B) 4d

C) 5d

D) 6d

✅ Answer

B) 4d

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9. Lanthanoid contraction causes 5d elements to be:

A) Much larger than 4d elements

B) Similar in size to corresponding 4d elements

C) Always smaller than 3d elements

D) Gases

✅ Answer

B) Similar in size to corresponding 4d elements.

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10. Which orbital is filled progressively across lanthanoids?

A) 2p

B) 3d

C) 4f

D) 5d

✅ Answer

C) 4f

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11. Which pair is most commonly cited as an example of similar sizes?

A) Zr and Hf

B) Na and Cs

C) Li and K

D) F and I

✅ Answer

A) Zr and Hf

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12. The size of lanthanoids from La to Lu generally:

A) Increases

B) Decreases

C) Remains constant

D) First increases then becomes zero

✅ Answer

B) Decreases

---

13. Which electrons provide poor shielding?

A) s-electrons

B) p-electrons

C) d-electrons only

D) 4f-electrons

✅ Answer

D) 4f-electrons

---

14. One consequence of lanthanoid contraction is:

A) Similarity between Zr and Hf

B) Large difference between Zr and Hf

C) Disappearance of 5d elements

D) Formation of alkali metals

✅ Answer

A) Similarity between Zr and Hf.

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15. Lanthanoid contraction is due to increasing:

A) Nuclear charge with poor 4f shielding

B) Number of shells without nuclear charge

C) Neutron loss

D) Atomic mass only

✅ Answer

A)

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16. Which series is directly affected in size by lanthanoid contraction?

A) 1s series

B) 2d series

C) 5d transition series

D) Hydrogen series

✅ Answer

C) 5d transition series

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17. Which statement is correct?

A) 4f electrons shield very effectively

B) 4f electrons shield poorly

C) 4f electrons do not exist

D) 4f electrons increase atomic radius greatly

✅ Answer

B)

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18. Due to lanthanoid contraction, separation of Zr and Hf is:

A) Easier because their properties are very different

B) Difficult because their properties are very similar

C) Impossible because both are gases

D) Unrelated to their sizes

✅ Answer

B)

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19. The main result of poor 4f shielding is:

A) Increased effective nuclear charge

B) Decreased proton number

C) Increased number of shells

D) Loss of nucleus

✅ Answer

A) Increased effective nuclear charge

---

20. The correct sequence is:

A) Poor 4f shielding → Effective nuclear charge ↑ → Atomic size ↓

B) Good 4f shielding → Size ↓

C) Poor 4f shielding → Nuclear charge ↓ → Size ↑

D) 4f shielding → No change in size

✅ Answer

A)

Q. What is lanthanoid contraction? Why does it occur?

Solution: Lanthanoid contraction is the gradual decrease in atomic and ionic radii from La to Lu. It occurs because the added 4f electrons have poor shielding ability, resulting in increased effective nuclear charge.

4f shielding ↓ → Effective nuclear charge ↑ → Radius ↓

Q. Explain the cause and one important effect of lanthanoid contraction.

Solution:

1. Electrons are progressively added to the 4f subshell from La to Lu.
2. 4f electrons shield the nuclear charge poorly.
3. Therefore, effective nuclear charge increases and atomic/ionic size decreases.
4. As a result, 5d elements such as Hf have sizes similar to their 4d congeners such as Zr.

Q. Explain lanthanoid contraction and its effect on the 5d series.

Step	Explanation
1	Atomic number increases across lanthanoids.
2	Electrons enter the 4f subshell.
3	4f electrons shield poorly.
4	Effective nuclear charge increases.
5	Lanthanoid atomic/ionic size decreases.
6	5d elements become similar in size to corresponding 4d elements.

Example: Zr and Hf have nearly identical atomic radii.

Q. Explain lanthanoid contraction and discuss its major consequences.

Solution:

Lanthanoid contraction is the gradual decrease in the atomic and ionic radii of lanthanoids from La to Lu. It results from the poor shielding effect of the 4f electrons.

• Effective nuclear charge increases across the lanthanoid series.
• Atomic and ionic radii gradually decrease.
• The expected increase in size of 5d elements is reduced.
• 5d elements have sizes similar to corresponding 4d elements.
• Zr and Hf therefore have very similar chemical properties.
• Separation of Zr and Hf is difficult.

Key Example: Zr ≈ Hf in atomic size.

Q. Explain the lanthanoid contraction in detail. Discuss its cause and its effect on the size and properties of 5d series elements.

Detailed Solution

The lanthanoids are a series of elements in which the 4f orbitals are progressively filled. From La to Lu, the atomic number increases and the nuclear charge also increases.

However, the newly added 4f electrons do not shield the outer electrons effectively because the shielding ability of 4f electrons is poor. Therefore, the effective nuclear charge experienced by the outer electrons increases.

Increasing nuclear charge + Poor 4f shielding → Increasing effective nuclear charge → Decreasing radius

Effect on 5d Series

After the lanthanoids, the 5d transition elements occur. Normally, the 5d elements should have considerably larger atomic radii than the corresponding 4d elements because their electrons occupy a higher principal shell.

But the contraction caused by the preceding lanthanoids offsets much of this expected increase. Consequently, the 5d elements have atomic and ionic radii very close to those of their corresponding 4d elements.

4d Element	5d Element	Effect
Zr	Hf	Very similar size
Nb	Ta	Very similar size
Mo	W	Very similar size
Ru	Os	Very similar size

Important Consequences

1. 5d elements have radii similar to their 4d counterparts.
2. Zr and Hf show very similar chemical properties.
3. Separation of Zr and Hf is difficult.
4. 5d elements generally have high densities because of their high atomic masses and relatively small atomic radii.

🎯 Final Answer:

Lanthanoid contraction is the gradual decrease in atomic and ionic radii from La to Lu due to the poor shielding effect of 4f electrons. This increases effective nuclear charge and pulls the electrons closer to the nucleus. As a consequence, the expected increase in size of the subsequent 5d transition elements is largely cancelled. Therefore, the 5d elements have atomic and ionic radii very similar to the corresponding 4d elements, with Zr and Hf being the classic example.

4f poor shielding → Lanthanoid contraction → 5d size ≈ 4d size

🎯 Quick Revision

La → Lu → Atomic/Ionic radius ↓
Reason: Poor shielding by 4f electrons
Effective Nuclear Charge: ↑
Important Effect: 5d size ≈ 4d size
Example: Zr ≈ Hf

CBSE Class 10 Social Science (087) Sample Paper 3 - 2026-27

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CBSE Sample Practice Paper — 3  (Session 2026–27)

Class: X (10th)

Subject: Social Science — Code: 087

Time: 3 Hours

Max. Marks: 80

Student Name: ______________________

Roll No.: __________

Section: __________

General Instructions:

1. This question paper is organised subject-wise into four parts: Part I — History, Part II — Geography, Part III — Political Science, and Part IV — Economics, each carrying 20 marks.

2. Each part contains four sections: Section 1 — Very Short Answer (MCQ, 1 mark each), Section 2 — Short Answer (3 marks each), Section 3 — Long Answer (5 marks), and Section 4 — Source/Case-Based Question (4 marks).

3. Internal choices have been provided in approximately one-third of the questions; attempt only one option wherever a choice is given.

4. All questions are compulsory unless an internal choice is indicated.

5. Marks for each question are indicated against it. Answer within the suggested word limit wherever applicable.

6. This is a practice paper prepared in line with the CBSE Class X Social Science (087) design for the 2026-27 session.

PART I — HISTORY   (20 Marks)

Section 1 — Very Short Answer (1 Mark each) — Q1 to Q5

Q1. Which term describes the sense of collective belonging that arises among people who see themselves as part of one nation? 1

(A) Colonialism(B) Nationalism(C) Imperialism(D) Federalism

Q2. Which revolutionary event in Europe is closely associated with the spread of the idea of nationalism in the early 19th century? 1

(A) The Industrial Revolution(B) The French Revolution(C) The Russian Revolution(D) The American Revolution

Q3. The Jallianwala Bagh massacre took place in which city? 1

(A) Lahore(B) Amritsar(C) Delhi(D) Ahmedabad

Q4. Which industrialist group's interests were significantly served by the Swadeshi call to boycott foreign goods during the freedom movement? 1

(A) Foreign investors(B) Indian industrialists(C) British planters(D) Foreign textile manufacturers

Q5. Name the pact under which Mahatma Gandhi agreed to participate in the Second Round Table Conference. 1

(A) Poona Pact(B) Gandhi-Irwin Pact(C) Lucknow Pact(D) Cripps Mission

Section 2 — Short Answer (3 Marks each) — Q6 to Q7

Q6. Explain any three ways in which the First World War created conditions favourable for the growth of a mass nationalist movement in India. 3

Q7. Describe the role of the industrial working class in the Civil Disobedience Movement. 3

— OR —

Explain how the Indian business classes reacted to the call for boycott of foreign goods during the national movement. 3

Section 3 — Long Answer (5 Marks) — Q8

Q8. Describe the various forms in which the idea of nationalism was expressed through the identification of India with "Bharat Mata," folklore, and icons/symbols during the freedom struggle. 5

— OR —

Explain the differing responses of various social groups — peasants, workers, and business classes — to the Non-Cooperation Movement, giving reasons for these differences. 5

Section 4 — Source-Based Question (4 Marks) — Q9

Q9. Read the following source and answer the questions that follow: 4

In April 1919, thousands of people gathered peacefully at Jallianwala Bagh in Amritsar, an enclosed ground with very few exits, to protest against the Rowlatt Act and the arrest of local leaders. General Dyer ordered his troops to open fire on the unarmed crowd without warning, resulting in the deaths of hundreds of men, women and children. The massacre shocked the nation and is widely regarded as a turning point that intensified anti-colonial sentiment across India, contributing directly to the launch of the Non-Cooperation Movement.

(i) In which city did the Jallianwala Bagh massacre take place? (1)

(ii) What was the immediate reason for the crowd gathering at Jallianwala Bagh? (1)

(iii) Explain how the massacre affected Indian public opinion and the course of the national movement. (2)

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PART II — GEOGRAPHY   (20 Marks)

Section 1 — Very Short Answer (1 Mark each) — Q10 to Q14

Q10. Which type of resource, based on the stock available, can be replenished by natural processes within a relatively short time? 1

(A) Non-renewable resource(B) Renewable resource(C) Abiotic resource(D) Potential resource

Q11. Which crop, requiring high temperature, high humidity and rainfall of over 200 cm, is best grown on the western coastal region of India? 1

(A) Wheat(B) Rice(C) Millets(D) Gram

Q12. India's first modern textile mill was established in which city? 1

(A) Kanpur(B) Mumbai(C) Ahmedabad(D) Kolkata

Q13. Which of the following is considered the most efficient and eco-friendly mode of transport for carrying bulky goods over long distances? 1

(A) Roadways(B) Waterways(C) Airways(D) Pipelines

Q14. Name the pollutant primarily responsible for water pollution when untreated sewage and industrial effluents are directly discharged into rivers. 1

(A) Organic and chemical pollutants(B) Radioactive waste only(C) Noise pollution(D) Air pollutants only

Section 2 — Short Answer (3 Marks each) — Q15 to Q16

Q15. Explain any three characteristics of the alluvial soils found in the northern plains of India. 3

Q16. Describe any three features of the Green Revolution and its impact on Indian agriculture. 3

— OR —

Explain any three reasons for the declining significance of railways for short-distance transport in India. 3

Section 3 — Long Answer (5 Marks) — Q17

Q17. Describe the role and importance of the "life-lines of national economy" — transport, communication and trade — in India's development. 5

— OR —

Explain the classification of industries on the basis of ownership, raw material, and size, with suitable examples of each. 5

Section 4 — Source-Based Question (4 Marks) — Q18

Q18. Read the following source and answer the questions that follow: 4

India's mineral wealth is unevenly distributed across the country, with certain regions being particularly rich in specific minerals. The Chotanagpur plateau region, spanning parts of Jharkhand, Odisha, and Chhattisgarh, is especially rich in iron ore, coal, and manganese, making it one of the most important mineral belts in the country. This concentration of resources has led to the establishment of major iron and steel plants in this region, taking advantage of the proximity of raw materials to reduce transportation costs.

(i) Name any one state that is part of the mineral-rich Chotanagpur plateau region. (1)

(ii) Name any two minerals found in abundance in this region. (1)

(iii) Explain why major iron and steel plants have been established close to this mineral belt. (2)

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PART III — POLITICAL SCIENCE   (20 Marks)

Section 1 — Very Short Answer (1 Mark each) — Q19 to Q23

Q19. Which system of power-sharing divides power among different social groups, often based on community or religion? 1

(A) Horizontal distribution(B) Community government(C) Vertical distribution(D) Unitary government

Q20. Which of the following is a key feature that distinguishes a federal system from a unitary system of government? 1

(A) Only one level of government exists(B) Power is constitutionally divided between different levels of government(C) Only the central government can make laws(D) States have no independent powers

Q21. Panchayati Raj institutions in India are an example of which tier of government? 1

(A) Union government(B) State government(C) Local government(D) None of these

Q22. Which of the following best describes a "political party"? 1

(A) A group of individuals seeking to gain power through elections to implement policies for the common good(B) A group formed to oppose all elections(C) A permanent government department(D) A judicial body

Q23. A political system in which political competition is restricted to one dominant party, with little space for meaningful opposition, is called a: 1

(A) Multi-party system(B) Two-party system(C) One-party system(D) No-party system

Section 2 — Short Answer (3 Marks each) — Q24 to Q25

Q24. Explain any three ways in which linguistic and religious diversity has been accommodated within India's federal system. 3

Q25. Describe any three functions performed by political parties in a democracy. 3

— OR —

Explain any three challenges commonly faced by political parties in a democracy today. 3

Section 3 — Long Answer (5 Marks) — Q26

Q26. Explain the constitutional provisions that make India a federal country, and describe how these provisions safeguard the powers of the states. 5

— OR —

Discuss the major challenges to democracy in contemporary times and suggest measures to strengthen democratic institutions. 5

Section 4 — Source-Based Question (4 Marks) — Q27

Q27. Read the following source and answer the questions that follow: 4

India's federal system divides governmental power between the Union government and the state governments, with certain subjects like defence and foreign affairs under the exclusive control of the Union, some subjects like agriculture and police under the states, and a few subjects like education and forests under joint control of both levels. This division of power, along with an independent judiciary to resolve disputes between different levels of government, has helped India manage its immense linguistic, religious, and regional diversity within a single political framework.

(i) Name one subject that falls under the exclusive control of the Union government. (1)

(ii) Name one subject that falls under the joint control of both the Union and state governments. (1)

(iii) Explain how India's federal structure has helped manage the country's diversity. (2)

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PART IV — ECONOMICS   (20 Marks)

Section 1 — Very Short Answer (1 Mark each) — Q28 to Q32

Q28. Which of the following best defines "per capita income"? 1

(A) Total income of a country(B) Average income earned per person in a country(C) Income of the richest person in a country(D) Government's total tax revenue

Q29. Which sector of the economy includes activities related to mining, agriculture, and fishing, based directly on natural resources? 1

(A) Primary sector(B) Secondary sector(C) Tertiary sector(D) Quaternary sector

Q30. Which of the following indicators is used to measure poverty in terms of a minimum acceptable standard of living? 1

(A) Literacy rate(B) Poverty line(C) Sex ratio(D) Infant mortality rate

Q31. Name the organisation, headed by the government of India, responsible for regulating the banking system and controlling the supply of money in the economy. 1

(A) SEBI(B) Reserve Bank of India(C) NITI Aayog(D) LIC

Q32. What term is used to describe the increasing interconnection of a country's economy with economies of other countries through trade and investment? 1

(A) Liberalisation(B) Globalisation(C) Privatisation(D) Nationalisation

Section 2 — Short Answer (3 Marks each) — Q33 to Q34

Q33. Explain any three reasons why average/per capita income alone is not considered a fully adequate indicator of a country's development. 3

Q34. Describe any three characteristics that distinguish the organised sector from the unorganised sector of the Indian economy. 3

— OR —

Explain any three ways in which the government can help promote employment growth in rural areas. 3

Section 3 — Long Answer (5 Marks) — Q35

Q35. Explain the meaning and significance of "sustainable development," and discuss why it is considered important, particularly with reference to the use of natural resources like groundwater. 5

— OR —

Discuss the role of multinational corporations (MNCs) in the process of globalisation, and explain how they influence production and investment decisions in countries like India. 5

Section 4 — Source-Based Question (4 Marks) — Q36

Q36. Read the following source and answer the questions that follow: 4

Consumer movements in India have gained strength over the decades, leading to the enactment of laws such as the Consumer Protection Act, which give buyers the right to seek redressal against unfair trade practices, exploitation, and defective goods or services. Consumer courts have been established at the district, state, and national levels to hear complaints and provide compensation where appropriate. Despite this progress, a large section of Indian consumers, especially in rural areas, remains unaware of their rights, limiting the full effectiveness of these legal protections.

(i) Name the Act that gives Indian consumers the right to seek redressal against unfair trade practices. (1)

(ii) At how many levels have consumer courts been established in India, according to the passage? (1)

(iii) Explain why a lack of consumer awareness limits the effectiveness of consumer protection laws, even when such laws exist. (2)

--- End of Question Paper --- All the best! ---

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Design of Question Paper — Blueprint & Analysis

1. Subject-wise (Part-wise) Marks Distribution

Part	Subject	Total Marks
I	History	20
II	Geography	20
III	Political Science	20
IV	Economics	20
Total		80

2. Section-wise Typology (per Part)

Section	Question Type	No. of Questions	Marks each	Marks per Part
1	Very Short Answer (MCQ)	5	1	5
2	Short Answer	2	3	6
3	Long Answer	1	5	5
4	Source-Based (1+1+2)	1	4	4
Total per Part				20

The same section-wise pattern (5+6+5+4 = 20 marks) is repeated identically across all four subject-wise parts, giving a paper total of 80 marks.

3. Competency-Level Distribution

Competency Level	Description	Approx. Marks	Percentage
Remembering & Understanding	Recall of facts, definitions, direct concept-based questions	40	50%
Applying	Application of concepts to explain, illustrate, or describe situations	24	30%
Analysing, Evaluating & Creating	Source-based reasoning, comparison, and evaluative long-answer questions	16	20%
Total		80	100%

4. Internal Choice Summary

Internal choices are provided in Q7, Q8, Q16, Q17, Q25, Q26, Q34 and Q35 — one question with a choice in Section 2 and Section 3 of every part, i.e. approximately one-third of the total questions across the paper.

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Answer Key

PART I — HISTORY

Q1. (B)   Q2. (B)   Q3. (B)   Q4. (B)   Q5. (B)

Q6. WWI led to forced recruitment causing resentment; sharp price rise/inflation created widespread economic hardship; increased taxes and war-related loans burdened the population, creating fertile ground for mass discontent and mobilisation (any three).

Q7. Industrial workers participated through strikes and by joining protest marches, though their involvement in the Civil Disobedience Movement was selective, as some workers absorbed nationalist ideas without fully accepting the Congress's core programme, especially regarding labour issues. OR: Indian business classes, organised through bodies like the Indian Industries and Commerce Congress and FICCI, largely supported the Swadeshi call as it protected them from foreign competition, though they later grew cautious about prolonged mass mobilisation that could threaten stability.

Q8. Nationalism was expressed through the personification of India as "Bharat Mata," a mother goddess figure evoking devotion and sacrifice; through revival of folklore, folk songs and traditions to build a shared cultural identity; and through icons like the tricolour flag, which became rallying symbols of the movement. OR: Peasants participated hoping for relief from land revenue and oppressive rents; workers joined seeking better wages and conditions, though the Congress leadership was cautious about fully embracing labour demands; business classes largely supported boycott of foreign goods for economic self-interest but grew wary as the movement grew increasingly assertive.

Q9. (i) Amritsar, Punjab. (ii) The crowd gathered to protest peacefully against the Rowlatt Act and the arrest of local nationalist leaders. (iii) The massacre outraged Indians across the country, discrediting British claims of just rule, turning many previously moderate Indians towards active resistance, and directly fuelling support for Gandhi's Non-Cooperation Movement.

PART II — GEOGRAPHY

Q10. (B)   Q11. (B)   Q12. (B)   Q13. (B)   Q14. (A)

Q15. Alluvial soils are highly fertile due to regular deposition by rivers, are rich in potash and lime but often deficient in nitrogen and phosphorus, and are ideal for crops like wheat, rice and sugarcane (any three points).

Q16. The Green Revolution led to a major increase in foodgrain production, especially wheat; it relied heavily on high-yielding variety (HYV) seeds, fertilisers and irrigation; but it was regionally concentrated (mainly Punjab, Haryana, western UP), leading to imbalanced agricultural growth (any three points). OR: Railways face competition from roads for short distances due to roads' door-to-door connectivity, lower cost for small loads, and greater flexibility in reaching remote or difficult terrain that railways cannot easily access.

Q17. Transport enables movement of raw materials, finished goods and people, connecting production and consumption centres; communication (including mass media) spreads information rapidly, aiding both economic coordination and social/political awareness; trade connects domestic markets with the global economy, contributing significantly to national income and employment. OR: By ownership: public sector (e.g., SAIL) vs private sector (e.g., TISCO); by raw material: agro-based (e.g., cotton textiles) vs mineral-based (e.g., iron and steel); by size: small-scale vs large-scale industries, each contributing differently to employment and output.

Q18. (i) Jharkhand (or Odisha/Chhattisgarh). (ii) Iron ore and coal (or manganese). (iii) Locating steel plants near these mineral deposits reduces the cost and time of transporting bulky raw materials, making production more economical and efficient.

PART III — POLITICAL SCIENCE

Q19. (B)   Q20. (B)   Q21. (C)   Q22. (A)   Q23. (C)

Q24. Formation of linguistic states based on the languages spoken in each region; constitutional recognition of multiple official languages; special provisions and autonomy for certain regions to protect their cultural and religious identity (any three).

Q25. Political parties contest elections and form governments; they act as a link between people and government, aggregating diverse demands into coherent policies; they provide access to welfare schemes and represent people's interests in the legislature (any three functions).

OR: Challenges: lack of internal democracy within parties, dynastic succession of leadership, growing influence of money and muscle power, and lack of meaningful choice due to declining ideological differences (any three).

Q26. India's constitution establishes two (or three, including local) levels of government with clearly defined powers under the Union, State, and Concurrent lists; changes to fundamental federal provisions require both Parliament and a majority of state legislatures to agree, and an independent judiciary resolves disputes between different levels — together these provisions protect the powers and autonomy of the states. OR: Challenges include the influence of money and criminalisation in politics, weakening of political institutions, and persistence of social inequalities; measures to strengthen democracy include electoral reforms, stronger anti-corruption mechanisms, and greater citizen participation and awareness.

Q27. (i) Defence (or foreign affairs/currency). (ii) Education (or forests). (iii) By clearly dividing subjects between different levels and allowing regional and linguistic groups a degree of self-governance within a unified constitutional framework, India's federal structure has accommodated its immense diversity while maintaining national unity.

PART IV — ECONOMICS

Q28. (B)   Q29. (A)   Q30. (B)   Q31. (B)   Q32. (B)

Q33. Per capita income is only an average, hiding inequalities in income distribution within a country; it does not reflect non-material aspects of well-being such as health, education, or environmental quality; and it can rise even while a large section of the population remains deprived (any three points).

Q34. The organised sector offers job security, regulated working hours, and social security benefits, unlike the unorganised sector, which is largely unregulated, offers no job security, and often provides low, irregular wages (any three points of comparison). OR: Government can promote rural employment by investing in rural infrastructure (roads, irrigation), setting up small-scale industries, and expanding schemes like MGNREGA to guarantee wage employment (any three measures).

Q35. Sustainable development refers to meeting present development needs without compromising the ability of future generations to meet their own needs; it is important because resources like groundwater are finite and can be exhausted by over-extraction, so responsible, regulated use is necessary to ensure resources remain available for the long term. OR: MNCs set up production units and offices across countries, often in collaboration with local companies, bringing capital, technology, and access to global markets, and significantly influencing production locations and investment decisions based on where costs are lowest and infrastructure is most favourable.

Q36. (i) The Consumer Protection Act. (ii) Three levels — district, state and national. (iii) Even with strong laws in place, consumers who are unaware of their rights are unlikely to file complaints or seek redressal when wronged, meaning the protections offered by the law remain underutilised, particularly among less-informed sections of society such as rural consumers.

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Detailed Marking Scheme

General Marking Guidelines

• Section 1 (MCQ): 1 mark for the correct option only; no partial credit.

• Section 2 (3-mark questions): 1 mark per valid point, up to a maximum of 3; each point should include a brief explanation, not just a label.

• Section 3 (5-mark questions): marks awarded for depth and range of explanation, relevant examples, and a well-organised answer covering multiple dimensions of the question.

• Section 4 (Source-based, 4 marks): each sub-part is marked independently as indicated (1, 1, 2); the 2-mark sub-part requires both a valid point and a clear explanation.

• Alternative correct points or examples not listed in the model answer should be given full credit if relevant and accurate.

Part-wise Mark Allocation Recap

Part	Section 1	Section 2	Section 3	Section 4	Total
I — History	5	6	5	4	20
II — Geography	5	6	5	4	20
III — Political Science	5	6	5	4	20
IV — Economics	5	6	5	4	20
Grand Total	20	24	20	16	80

This sample paper, blueprint, and answer key are prepared for CBSE Class X Social Science (087) practice, Session 2026-27, organised subject-wise into separate parts for History, Geography, Political Science and Economics, in line with the current CBSE Question Paper Design guidelines.

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Compare the size of a neutral atom with its Cation and Anion.

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Detailed Explanation

🔵 Basic Comparison

The size of an atom changes when it gains or loses electrons. Therefore, the radius of a neutral atom is different from the radius of its cation or anion.

Cation < Neutral Atom < Anion

Positive ion  <  Neutral atom  <  Negative ion

🔴 Cation – Smaller than Neutral Atom

A cation is formed when a neutral atom loses one or more electrons.

After losing electrons, the number of electrons decreases while the nuclear charge remains the same. In many cases, the outermost shell is completely lost. Hence, the remaining electrons are attracted more strongly towards the nucleus.

Neutral Atom → Loss of e⁻ → Cation → Size Decreases

Example:

Na → Na⁺ + e⁻

The sodium atom is larger than the sodium ion:

Na > Na⁺

🟢 Anion – Larger than Neutral Atom

An anion is formed when a neutral atom gains one or more electrons.

The nuclear charge remains unchanged, but the number of electrons increases. This increases electron-electron repulsion and reduces the effective attraction experienced by each electron. Therefore, the electron cloud expands.

Neutral Atom → Gain of e⁻ → Anion → Size Increases

Example:

Cl + e⁻ → Cl⁻

The chloride ion is larger than the chlorine atom:

Cl < Cl⁻

📊 Comparison Table

Species	Electron Change	Effect on Size	Reason
Cation (+)	Loss of electrons	Smaller	Greater effective attraction and often loss of outer shell
Neutral Atom	No gain/loss	Reference size	Normal balance of nuclear attraction and electron repulsion
Anion (−)	Gain of electrons	Larger	Greater electron-electron repulsion

🔬 Example with Isoelectronic Species

Consider Na⁺, Ne and F⁻. All three species have 10 electrons, but their nuclear charges are different.

Na⁺  ,  Ne  ,  F⁻

Na⁺ has the greatest nuclear charge among these three and therefore has the smallest radius, while F⁻ has the lowest nuclear charge and the largest radius.

Na⁺ < Ne < F⁻

✅ Final Answer

A cation is smaller than its neutral atom because it loses electrons, whereas an anion is larger because it gains electrons and experiences increased electron-electron repulsion.

Cation < Neutral Atom < Anion

📝 20 MCQs with Answers

1. Which is generally the smallest?

A) Anion

B) Neutral atom

C) Cation

D) All are equal

✅ Answer

C) Cation

---

2. A cation is formed by:

A) Gain of electrons

B) Loss of electrons

C) Gain of neutrons

D) Gain of protons only

✅ Answer

B) Loss of electrons

---

3. An anion is generally ______ than its neutral atom.

A) Smaller

B) Larger

C) Equal

D) Massless

✅ Answer

B) Larger

---

4. A cation is generally ______ than its neutral atom.

A) Larger

B) Smaller

C) Equal

D) Unstable only

✅ Answer

B) Smaller

---

5. Which sequence is generally correct?

A) Anion < Atom < Cation

B) Cation < Atom < Anion

C) Atom < Cation < Anion

D) Cation = Atom = Anion

✅ Answer

B) Cation < Atom < Anion

---

6. What happens to the number of electrons when a cation forms?

A) Increases

B) Decreases

C) Remains unchanged

D) Doubles

✅ Answer

B) Decreases

---

7. What happens to the number of electrons when an anion forms?

A) Decreases

B) Increases

C) Becomes zero

D) Remains unchanged

✅ Answer

B) Increases

---

8. Which ion is smaller than Na?

A) Na⁺

B) Na⁻

C) Both are larger

D) None

✅ Answer

A) Na⁺

---

9. Which ion is larger than Cl?

A) Cl⁺

B) Cl⁻

C) Both are smaller

D) Neither

✅ Answer

B) Cl⁻

---

10. Formation of an anion increases:

A) Electron-electron repulsion

B) Proton number

C) Nuclear charge

D) Atomic number

✅ Answer

A) Electron-electron repulsion

---

11. During ion formation, the number of protons generally:

A) Changes

B) Remains unchanged

C) Becomes zero

D) Doubles

✅ Answer

B) Remains unchanged

---

12. Which has greater electron-electron repulsion?

A) Anion

B) Cation

C) Proton

D) Nucleus

✅ Answer

A) Anion

---

13. The radius of Na⁺ is smaller than Na because:

A) Na⁺ gains electrons

B) Na⁺ loses an electron and has stronger effective attraction

C) Na⁺ gains a shell

D) Nuclear charge disappears

✅ Answer

B)

---

14. The radius of Cl⁻ is larger than Cl because:

A) It loses electrons

B) It gains an electron

C) It loses protons

D) It loses a shell

✅ Answer

B) It gains an electron

---

15. Which species has a positive charge?

A) Anion

B) Cation

C) Neutral atom

D) Isotope

✅ Answer

B) Cation

---

16. Which species has a negative charge?

A) Cation

B) Anion

C) Neutral atom

D) Nucleus

✅ Answer

B) Anion

---

17. Which has the largest radius in the simple comparison?

A) Cation

B) Neutral atom

C) Anion

D) Nucleus

✅ Answer

C) Anion

---

18. Correct order for size is:

A) Cl⁻ < Cl < Cl⁺

B) Cl⁺ < Cl < Cl⁻

C) Cl < Cl⁻ < Cl⁺

D) All equal

✅ Answer

B) Cl⁺ < Cl < Cl⁻

---

19. Which statement is correct?

A) Cations are generally larger than atoms

B) Anions are generally smaller than atoms

C) Cations are generally smaller and anions generally larger than their parent atoms

D) Ion formation never affects size

✅ Answer

C)

---

20. The correct general relationship is:

A) Cation > Atom > Anion

B) Anion > Atom > Cation

C) Atom > Anion > Cation

D) Cation = Atom = Anion

✅ Answer

B) Anion > Atom > Cation

Q. Compare the size of a neutral atom with its cation and anion.

Solution:

• A cation is smaller than its neutral atom because it loses electrons.
• An anion is larger than its neutral atom because it gains electrons, increasing electron-electron repulsion.

Cation < Neutral Atom < Anion

Q. Explain why cations are smaller and anions are larger than their parent atoms.

Solution:

1. Cation: Loss of electrons reduces electron-electron repulsion and may remove the outermost shell, making the ion smaller.
2. Anion: Gain of electrons increases electron-electron repulsion, causing expansion of the electron cloud.
3. The number of protons does not change during ordinary ion formation.

Therefore: Cation < Neutral Atom < Anion

Q. Differentiate between the size of a neutral atom, cation and anion.

Species	Electron Change	Relative Size	Main Reason
Cation	Loses e⁻	Smaller	Greater effective attraction; possible loss of outer shell
Neutral Atom	No change	Normal	Reference size
Anion	Gains e⁻	Larger	Increased electron-electron repulsion

Size order: Cation < Neutral Atom < Anion

Q. Explain the change in atomic size when an atom forms a cation or an anion.

Solution:

Formation of Cation

When an atom loses one or more electrons, a positive ion called a cation is formed. The number of protons remains unchanged, but the number of electrons decreases. The remaining electrons experience stronger attraction from the nucleus. If the complete outer shell is lost, the decrease in size is even more significant.

Formation of Anion

When an atom gains one or more electrons, a negative ion called an anion is formed. The nuclear charge remains unchanged, but electron-electron repulsion increases. Consequently, the electron cloud expands and the ionic radius becomes larger.

Cation < Neutral Atom < Anion

Q. Compare the size of a neutral atom, its cation and anion. Explain the reasons with suitable examples.

Detailed Solution

The size of an atom or ion is expressed in terms of its atomic or ionic radius. Formation of an ion involves the loss or gain of electrons, while the number of protons remains unchanged. This produces a significant change in size.

1. Cation

A cation is formed by the loss of electrons. Since the nuclear charge remains the same but fewer electrons are present, the attraction between the nucleus and the remaining electrons becomes stronger. In some cases, the entire outermost shell is removed.

Na → Na⁺ + e⁻
Na⁺ is smaller than Na.

2. Neutral Atom

A neutral atom has an equal number of protons and electrons. Its size lies between the sizes of its corresponding cation and anion in the simple comparison.

3. Anion

An anion is formed by gaining electrons. Since the nuclear charge remains unchanged but the number of electrons increases, electron-electron repulsion increases. The electron cloud expands and the ionic radius increases.

Cl + e⁻ → Cl⁻
Cl⁻ is larger than Cl.

📊 Overall Comparison

Species	Electron Change	Size
Cation (+)	Loss	Smallest
Neutral Atom	No change	Intermediate
Anion (−)	Gain	Largest

🎯 Final Answer:

A cation is generally smaller than its neutral atom because it loses electrons and experiences stronger effective nuclear attraction. An anion is generally larger because it gains electrons, increasing electron-electron repulsion and expanding the electron cloud.

Cation < Neutral Atom < Anion

🎯 Quick Revision

Lose e⁻ → Cation → Size ↓
Neutral Atom → Normal Size
Gain e⁻ → Anion → Size ↑

Cation < Neutral Atom < Anion