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NEET levelSingle correct optionDifficulty 1 of 3pt121

The second electron gain enthalpy of oxygen, for $O X^{-} (g) + e^{-} \to O X^{2 -} (g)$ , is positive because

A $O X^{-}$ has a noble gas configuration
Boxygen has a half-filled $2 p$ subshell
Can electron is being added to an already negatively charged ion and repulsion must be overcome
Doxygen has a very low nuclear charge

Answer: C

O X^{-}

is

2 s^{2} 2 p^{5}

, and the new electron is repelled by the net negative charge. This repulsion outweighs the attraction of the nucleus, so the step is endothermic (about +

744 kJ mo l^{- 1}

).

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