Question

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

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

Answer 1

Answer: (B)

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.