Question

If two non-metallic elements $X$ and $Y$ have $L$ and $M$ shells as valence shells, respectively with the same no. of electrons. Then, between $X$ and $Y$ which one has a greater electron affinity?

Answer 1

As the size of the atom increases, the distance between the nucleus and the last shell which receives the incoming electrons increases. Due to this the force of attraction between the nucleus and the incoming electron decreases and thus the electron gain enthalpy becomes less negative. But there is an exception in the case of L and M shell.

Given that $X$ has $L$ shells while the $Y$ have $M$ shells as valence shells, i.e., $X$ is smaller in size, but $Y$ has greater electron affinity due to high electron-electron repulsion in case of X.

So, the correct answer is Y.