Question

Among $O , O ^{+}, O ^{2+}$ and $O ^{2-}$, the species having most positive and most negative value of $\Delta H _{ eg }$ are respectively.

• A. $O ^{+}$and $O$
• B. $O ^{2+}$ and $O ^{2-}$
• C. $O$ anḍ $O ^{2-}$
• D. $O ^{2-}$ and $O ^{2+}$

Answer 1

Answer: (D)

Successive electron affinity always decrease
$O \xrightarrow{+ e }O ^{-} \Delta H_{ eg }=(-) ve$
$ O ^{-} \xrightarrow{+ e } O ^{2-} \Delta H_{ eg }=(+) ve $
$ O \xrightarrow{+2 e }O ^{2-} \Delta H_{ eg }(\text { Total })=(+) ve$
Thus, $O ^{2-}$ will show most positive $\Delta H _{ eg }$, while $O ^{2+}$ will show most negative value due to small size.