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
$O\stackrel{+e}{\to }{O}^{-}\Delta H_{eg}=(-)ve$
$O^{-}\stackrel{+e}{\to }{O}^{2-}\Delta H_{eg}=(+)ve$
$O\stackrel{+2e}{\to }{O}^{2-}\Delta H_{eg}(\text{ Total })=(+)ve$
Thus, $O^{2-}$ will show most positive $\Delta H_{eg}$, while $O^{2+}$ will show most negative value due to small size.