Which group has the most negative electron gain enthalpy?

1. Which group has the most negative electron gain enthalpy? +

Correct Answer

Group 17 — Halogens

Detailed Explanation

Electron gain enthalpy is the enthalpy change when an isolated gaseous atom accepts an electron:

X(g) + e⁻ → X⁻(g)

For Group 17 elements, the outer electronic configuration is:

ns² np⁵

They need only one electron to achieve the stable noble-gas configuration:

ns² np⁵ + e⁻ → ns² np⁶

Therefore, electron addition is highly favourable and a large amount of energy is released. Hence, their electron gain enthalpy is strongly negative.

Group 17 → Most negative electron gain enthalpy

Important Exception: Fluorine vs Chlorine

Although fluorine is the most electronegative element, chlorine has a more negative electron gain enthalpy than fluorine. The reason is the very small size of fluorine. The incoming electron enters the compact 2p orbital, where electron–electron repulsion is high. In chlorine, the electron enters the larger 3p orbital, where repulsion is comparatively lower.

Δ_egH(Cl) < Δ_egH(F)

Thus, among halogens, chlorine has the most negative electron gain enthalpy.

Periodic Trend

The general trend is:

Group 17 > other groups in tendency to gain an electron

For the halogens, the magnitude generally decreases down the group, with fluorine showing the well-known anomaly:

Cl > F > Br > I

where the comparison refers to the magnitude of energy released / negativity of electron gain enthalpy.

JEE / NEET Shortcut

If the question asks: “Which group has the most negative electron gain enthalpy?” Remember:

Group 17 = Halogens = ns²np⁵ = need 1 electron

So the answer is:

Group 17 (Halogens)

30 Related MCQs with Solutions

1. Which group generally has the most negative electron gain enthalpy?

A. Group 1

B. Group 2

C. Group 17

D. Group 18

Answer: C. Group 17
Halogens need one electron to complete their octet.

2. The valence-shell configuration of Group 17 elements is:

A. ns¹

B. ns²

C. ns²np⁵

D. ns²np⁶

Answer: C. ns²np⁵

3. Group 17 elements readily gain:

A. One electron

B. Two electrons

C. One proton

D. One neutron

Answer: A

4. Which halogen has the most negative electron gain enthalpy?

A. F

B. Cl

C. Br

D. I

Answer: B. Cl

5. Fluorine has the highest:

A. Atomic radius

B. Electronegativity

C. Metallic character

D. Shielding effect

Answer: B. Electronegativity

6. Why is Cl electron gain enthalpy more negative than F?

A. Cl has smaller size

B. F has greater 2p electron repulsion

C. Cl has lower nuclear charge

D. F has no p electrons

Answer: B

7. Electron gain enthalpy is associated with:

A. Removal of an electron

B. Addition of an electron

C. Removal of a proton

D. Addition of a neutron

Answer: B

8. A negative electron gain enthalpy indicates that:

A. Energy is released

B. Energy is always absorbed

C. No energy change occurs

D. Atom loses a proton

Answer: A

9. Which configuration is one electron short of a noble-gas configuration?

A. ns¹

B. ns²np⁵

C. ns²np⁶

D. ns²np²

Answer: B

10. Which element has the most negative electron gain enthalpy among F and Cl?

A. F

B. Cl

C. Both equal

D. Cannot be predicted

Answer: B. Cl

11. Group 18 elements generally have very low tendency to:

A. Gain an electron

B. Exist as gases

C. Form atoms

D. Have electrons

Answer: A

12. Which group contains halogens?

A. Group 1

B. Group 2

C. Group 17

D. Group 18

Answer: C

13. The electron gain process for chlorine is:

A. Cl → Cl⁺ + e⁻

B. Cl + e⁻ → Cl⁻

C. Cl → Cl²⁺

D. Cl + p⁺ → Cl⁺

Answer: B

14. Which orbital receives the incoming electron in Cl?

A. 2p

B. 3s

C. 3p

D. 4s

Answer: C. 3p

15. Which factor generally makes electron gain more favourable?

A. Very stable closed shell

B. Nearly complete valence shell

C. Very large atomic radius only

D. Complete octet

Answer: B

16. Which element has configuration [Ne]3s²3p⁵?

A. F

B. Cl

C. Br

D. O

Answer: B. Cl

17. Which group is known as the halogen group?

A. 13

B. 14

C. 16

D. 17

Answer: D. Group 17

18. Which element has an almost complete octet?

A. Na

B. Mg

C. Cl

D. Ne

Answer: C. Cl

19. Which species has a stable noble-gas configuration after gaining one electron?

A. Na

B. Cl

C. Ne

D. Mg

Answer: B. Cl

20. Electron gain enthalpy is usually expressed in:

A. kJ mol⁻¹

B. kg mol⁻¹

C. mol L⁻¹

D. atm

Answer: A. kJ mol⁻¹

21. Which is more negative: −349 kJ mol⁻¹ or −328 kJ mol⁻¹?

A. −349 kJ mol⁻¹

B. −328 kJ mol⁻¹

C. Both equal

D. Neither

Answer: A. −349 kJ mol⁻¹

22. Which factor can reduce electron–electron repulsion in an incoming electron?

A. Larger orbital size

B. Smaller orbital size

C. Higher electron density

D. Greater crowding

Answer: A

23. Which group generally shows high electron affinity tendency?

A. Alkali metals

B. Halogens

C. Noble gases

D. Alkaline earth metals

Answer: B. Halogens

24. Which has greater electronegativity?

A. F

B. Cl

C. Br

D. I

Answer: A. F

25. Which statement is correct?

A. F has the most negative electron gain enthalpy

B. Cl has more negative electron gain enthalpy than F

C. Noble gases have the most negative values

D. Group 1 always has the most negative values

Answer: B

26. Why do noble gases resist electron addition?

A. They have incomplete shells

B. They have stable closed-shell configurations

C. They have one valence electron

D. They are all metals

Answer: B

27. The most favourable electron addition among the following is generally associated with:

A. ns²np⁵

B. ns²np⁶

C. ns²

D. ns¹

Answer: A

28. Which halogen is the largest in size?

A. F

B. Cl

C. Br

D. I

Answer: D. I

29. Which statement best explains Group 17 electron gain enthalpy?

A. They need one electron to complete the valence shell

B. They need seven electrons

C. They already have a complete shell

D. They easily lose electrons

Answer: A

30. The correct answer to the original question is:

A. Group 1

B. Group 2

C. Group 17

D. Group 18

Answer: C. Group 17 — Halogens

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