Question

Assertion $\left(A\right):$ Electron gain enthalpy becomes less negative as we go down a group.

Reason $\left(R\right):$ Size of the atom increases on going down the group and the added electron would be farther from the nucleus.

• A. Assertion and reason both are correct statements and reason is the correct explanation of assertion.
• B. Assertion is a wrong statement but the reason is correct.
• C. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
• D. Assertion and reason both are wrong statements.

Answer 1

The correct option is B

Assertion is a wrong statement but the reason is correct.

Analysing the assertion

Generally, electron gain enthalpy becomes less negative (decreases) as we go down the group because size of the atom increases, and the added electron will be farther from the nucleus. So, lesser energy will be released on gain of electron.

But it does not always become less negative as we go down a group in Modern periodic table.

For Example: ${△}_{eg}H\left(F\right)<{△}_{eg}H\left(Cl\right).$

Electron gain enthalpy of fluorine is less negative than chlorine due to high inter electronic repulsion because of small size of $F$

So, the assertion is not true.

Analysing the reason

The size of the atom increases on going down the group and the added electron would be farther from the nucleus (As on moving down the group the number of shell increases). So, lesser energy will be released on gain of electron.

Thus the statement given in reason is true.

Conclusion:

On the basis of the above analysis, we can say that assertion is a wrong statement, but the reason is the correct.

Hence option $\left(D\right)$ is correct.