JEE Main · 2020 · 04 Sep 2020 · Shift 2 · Classification of Elements and Periodicity

The process that is NOT endothermic in nature is:

(A) $H_{(g)} + e^{-} \to H_{(g)}^{-}$ ✓ Correct
(B) $O_{(g)}^{-} + e^{-} \to O_{(g)}^{2 -}$
(C) $Na_{(g)} \to Na_{(g)}^{+} + e^{-}$
(D) $Ar_{(g)} + e^{-} \to Ar_{(g)}^{-}$

Answer: (A)

Solution

Adding an electron to a neutral hydrogen atom,

H_{(g)} + e^{-} \to H_{(g)}^{-}

, completes a stable

1 s^{2}

shell and releases energy, so this process is exothermic. By contrast, forcing a second electron onto the already negative

O^{-}

to make

O^{2 -}

costs energy, removing an electron from sodium is its ionisation and is endothermic, and adding an electron to a closed-shell argon atom is also endothermic. The only process that is not endothermic is the electron gain by hydrogen.

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JEE Main · 2020 · 04 Sep 2020 · Shift 2 · Classification of Elements and Periodicity

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