JEE Chemistry 2024 Question with Solution

Given: The elements are $\text{Ar}$, $\text{Br}$, $\text{F}$, and $\text{S}$.

Find: The correct sequence of electron gain enthalpy.

Understanding Electron Gain Enthalpy: Electron gain enthalpy is the amount of energy released when an electron is added to a neutral atom in the gaseous state to form a negative ion. Higher negative values indicate that an element releases more energy when gaining an electron.

From the extracted solution table:

$$\begin{aligned} \text{F} & : -333 \, \text{kJ/mol} \\ \text{S} & : -200 \, \text{kJ/mol} \\ \text{Br} & : -325 \, \text{kJ/mol} \\ \text{Ar} & : +96 \, \text{kJ/mol} \end{aligned}$$

Therefore, in decreasing order as concluded in the source solution:

$$\text{Ar} > \text{S} > \text{Br} > \text{F}$$

This corresponds to $A > D > B > C$.

Therefore, the correct option is B.

Given: We need to compare electron gain enthalpy for $\text{Ar}$, $\text{Br}$, $\text{F}$, and $\text{S}$.

Find: Which option gives the correct sequence.

The source solution states:

• $\text{Ar}$ is a noble gas and has negligible electron affinity.
• $\text{F}$ has high electron affinity.
• $\text{Br}$ also has high electron affinity.
• $\text{S}$ has moderate electron affinity.

The second approach provides the numerical values directly, so we use those values as the authority:

$$\Delta_{eg}H(\text{F}) = -333 \, \text{kJ/mol}$$ $$\Delta_{eg}H(\text{S}) = -200 \, \text{kJ/mol}$$ $$\Delta_{eg}H(\text{Br}) = -325 \, \text{kJ/mol}$$ $$\Delta_{eg}H(\text{Ar}) = +96 \, \text{kJ/mol}$$

Arranging according to the sequence stated in the source solution gives:

$$A > D > B > C$$

Thus, the correct answer is Option 2, that is, B.