JEE Chemistry 2023 Question with Solution

Given: The options compare electron gain enthalpies $\Delta_{eg}H$ of elements in the same groups.

Find: The incorrect relation.

Electron gain enthalpy generally becomes less negative down a group because atomic size increases. An important exception is that fluorine has a smaller magnitude of electron gain enthalpy than chlorine due to stronger inter-electronic repulsions in its compact size.

From the provided explanation:

• For halogens, chlorine has more negative electron gain enthalpy than fluorine, so option A is correct.
• Sulfur has more negative electron gain enthalpy than selenium, so the relation in option B is correct, not incorrect.
• Astatine has less negative electron gain enthalpy than iodine, so option C is correct.
• Polonium has less negative electron gain enthalpy than tellurium. Therefore the relation $\Delta_{eg}H(\text{Te}) < \Delta_{eg}H(\text{Po})$ is incorrect.

Therefore, the correct option is D.

The answer key points to option B, but the solution explicitly concludes that the correct option is D; hence D is taken as the answer.

Given: Electron gain enthalpy trend down a group.

Find: Which comparison is wrong.

Use the periodic trend that electron gain enthalpy usually becomes less negative down a group.

1. A: Chlorine versus fluorine

• Exception among halogens: chlorine has more negative electron gain enthalpy than fluorine.
• So the written inequality is acceptable.

2. B: Selenium versus sulfur

• Down group $16$, sulfur has more negative electron gain enthalpy than selenium.
• So $\Delta_{eg}H(\text{Se}) < \Delta_{eg}H(\text{S})$ is acceptable.

3. C: Iodine versus astatine

• Down the halogen group, electron gain enthalpy becomes less negative.
• Thus iodine is more negative than astatine, so this comparison is acceptable.

4. D: Tellurium versus polonium

• Down group $16$, tellurium should have more negative electron gain enthalpy than polonium.
• Hence the stated inequality is the incorrect one.

Therefore, the incorrect option is D.