Question

Arrange S , O , and Se in ascending order of electron affinity

• A. S < Se < O
• B. Se < O < S
• C. S < O < Se
• D. O < Se < S

Answer 1

Answer: (D)

$S,O$ and Se are all $16^{\text{th }}$ group elements.
Since electron affinity generally decreases down the period. So, the expected order would be $O>S>Se$

But this is not the observed case. The reason for this is that the oxygen atom is extremely small.
Therefore it cannot hold a negative charge in such a small space. Thus, its electron affinity is the lowest in its group. So, the correct order will be: $O<$ Se $<S$