Basic strength of hydroxides of Group 1 elements follows what order?

1. Basic strength of hydroxides of Group 1 elements follows what order? +

Correct Answer

LiOH < NaOH < KOH < RbOH < CsOH

Why does basic strength increase down Group 1?

The hydroxides of Group 1 are:

LiOH → NaOH → KOH → RbOH → CsOH

As we move down the group, the size of the alkali-metal ion increases and the M–OH bond becomes weaker. Therefore, the hydroxide ion, OH⁻, is released more readily in aqueous solution.

Down the group → M⁺ size ↑ → M–OH bond strength ↓ → OH⁻ availability ↑ → Basicity ↑

Hence:

LiOH < NaOH < KOH < RbOH < CsOH

Important Concept

Group 1 hydroxides are generally strong bases, and their basic strength increases down the group. LiOH is the least basic among them, while CsOH is the strongest. The trend is mainly associated with increasing ionic size and decreasing lattice/bonding strength, which makes hydroxide formation or dissociation easier.

Basic strength ∝ Ease of OH⁻ release

JEE / NEET Shortcut

Group 1: Basicity increases downward ↓

LiOH < NaOH < KOH < RbOH < CsOH

Memory Trick:

Li → Na → K → Rb → Cs
Basic strength: increasing ↓

Do not confuse this with the thermal stability of Group 1 hydroxides, which also generally increases down the group.

30 Related MCQs with Solutions

1. The correct order of basic strength of Group 1 hydroxides is:

A. CsOH < RbOH < KOH < NaOH < LiOH

B. LiOH < NaOH < KOH < RbOH < CsOH

C. NaOH < LiOH < KOH < CsOH < RbOH

D. KOH < NaOH < LiOH < RbOH < CsOH

Answer: B

2. Which is the strongest base among the following?

A. LiOH

B. NaOH

C. KOH

D. CsOH

Answer: D. CsOH

3. Which Group 1 hydroxide has the lowest basic strength?

A. LiOH

B. NaOH

C. RbOH

D. CsOH

Answer: A. LiOH

4. On moving down Group 1, basic strength of hydroxides:

A. Decreases

B. Increases

C. Remains constant

D. First increases then decreases

Answer: B. Increases

5. Which factor contributes to increasing basic strength down Group 1?

A. Increasing lattice/bonding weakness

B. Increasing electronegativity

C. Decreasing ionic size

D. Increasing ionization enthalpy

Answer: A

6. The basicity of an alkali-metal hydroxide is related to the availability of:

A. H⁺

B. OH⁻

C. e⁻

D. O²⁻

Answer: B. OH⁻

7. Which hydroxide is more basic?

A. LiOH

B. KOH

C. Both equal

D. Cannot be predicted

Answer: B. KOH

8. The M–OH bond generally becomes ______ down Group 1.

A. Stronger

B. Weaker

C. Unchanged

D. Covalent only

Answer: B. Weaker

9. Which sequence represents increasing basic strength?

A. CsOH < RbOH < KOH

B. LiOH < NaOH < KOH

C. KOH < LiOH < NaOH

D. NaOH < CsOH < LiOH

Answer: B

10. Which ion becomes larger down Group 1?

A. H⁺

B. M⁺

C. OH⁻

D. O²⁻

Answer: B. M⁺

11. Which hydroxide is the strongest base among these?

A. NaOH

B. KOH

C. RbOH

D. CsOH

Answer: D. CsOH

12. Which hydroxide is least basic?

A. CsOH

B. RbOH

C. LiOH

D. KOH

Answer: C. LiOH

13. Basic strength down Group 1 is mainly associated with:

A. Increasing metallic character and easier OH⁻ release

B. Decreasing metallic character

C. Increasing electronegativity

D. Increasing ionization enthalpy

Answer: A

14. Which is a Group 1 hydroxide?

A. Mg(OH)₂

B. Al(OH)₃

C. KOH

D. Ca(OH)₂

Answer: C. KOH

15. Which order is correct for increasing ionic radius?

A. Cs⁺ < Rb⁺ < K⁺

B. Li⁺ < Na⁺ < K⁺ < Rb⁺ < Cs⁺

C. K⁺ < Li⁺ < Cs⁺

D. Na⁺ < Li⁺ < Cs⁺

Answer: B

16. Strong bases generally produce a high concentration of:

A. H⁺

B. OH⁻

C. Cl⁻

D. Na⁺ only

Answer: B. OH⁻

17. Which is stronger as a base?

A. LiOH

B. RbOH

C. Both are identical

D. LiOH only in every solvent

Answer: B. RbOH

18. The solubility of Group 1 hydroxides generally:

A. Increases down the group

B. Decreases down the group

C. Remains identical

D. Becomes zero

Answer: A. Increases down the group

19. Which Group 1 hydroxide is commonly considered the strongest base?

A. LiOH

B. NaOH

C. KOH

D. CsOH

Answer: D. CsOH

20. Which property increases down Group 1?

A. Ionization enthalpy

B. Electronegativity

C. Metallic character

D. Atomic attraction for electrons

Answer: C. Metallic character

21. The correct order of basicity is:

A. LiOH < NaOH < KOH

B. KOH < NaOH < LiOH

C. NaOH < LiOH < KOH

D. LiOH = NaOH = KOH

Answer: A

22. Which hydroxide has the greatest ease of dissociation among these?

A. LiOH

B. NaOH

C. KOH

D. CsOH

Answer: D. CsOH

23. Group 1 elements are also called:

A. Halogens

B. Alkali metals

C. Alkaline earth metals

D. Noble gases

Answer: B. Alkali metals

24. Which hydroxide is least soluble among the following Group 1 hydroxides?

A. LiOH

B. NaOH

C. KOH

D. CsOH

Answer: A. LiOH

25. Increasing basicity down Group 1 is consistent with increasing:

A. Atomic size

B. Ionization enthalpy

C. Electronegativity

D. Electron affinity

Answer: A. Atomic size

26. Which statement is correct?

A. LiOH is stronger than CsOH

B. CsOH is stronger than LiOH

C. All Group 1 hydroxides have identical basic strength

D. NaOH is the weakest

Answer: B. CsOH is stronger than LiOH

27. Which factor decreases down Group 1?

A. Atomic size

B. Metallic character

C. Ionization enthalpy

D. Basic strength of hydroxides

Answer: C. Ionization enthalpy

28. The strongest commonly used aqueous Group 1 hydroxide base among these is:

A. LiOH

B. NaOH

C. KOH

D. CsOH

Answer: D. CsOH

29. Basic strength of Group 1 hydroxides is:

A. LiOH > NaOH > KOH > RbOH > CsOH

B. LiOH < NaOH < KOH < RbOH < CsOH

C. LiOH = NaOH = KOH = RbOH = CsOH

D. NaOH > LiOH > CsOH

Answer: B

30. The key trend to remember for Group 1 hydroxides is:

A. Basicity decreases down the group

B. Basicity increases down the group

C. Basicity is independent of position

D. Basicity first increases and then decreases

Answer: B. Basicity increases down the group

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