Question

Within each pair of element $F$ & $Cl,S$ & $Se$ and $Li$ & $Na$, respectively, the elements that release more energy upon electron gain are :

• A. $Cl,S$ and $Li$
• B. $F,Se$ and $Na$
• C. $Cl,Se$ and $Na$
• D. $F,S$ and $Li$

Answer 1

The correct option is A $Cl,S$ and $Li$

Down the group electron affinity decrease due to increasing size. So, the electron affinity of $S>Se$ and $Li>Na$ so energy release will also be more. But in case of $F$ and $Cl,$ there is exception, $Cl>F.$ It is due to the small size of $F$ atom where the incoming electron face high electron-electron repulsion, So, the energy release will be more in $Cl$.
Correct option is (a).