How many of the following are exothermic changes?
(A) $N_{(g)} + e^{-} \to N_{(g)}^{-}$ (B) $Li_{(g)} + e^{-} \to Li_{(g)}^{-}$
(c) $Be_{(g)} + e^{-} \to Be_{(g)}^{-}$ (D) $Mg_{(g)} + e^{-} \to Mg_{(g)}^{-}$
(E) $B_{(g)} + e^{-} \to B_{(g)}^{-}$ (F) $O_{(g)}^{-} + e^{-} \to O_{(g)}^{2 -}$

Question

How many of the following are exothermic changes?

(A) $N_{(g)} + e^{-} \to N_{(g)}^{-}$ (B) $Li_{(g)} + e^{-} \to Li_{(g)}^{-}$

(c) $Be_{(g)} + e^{-} \to Be_{(g)}^{-}$ (D) $Mg_{(g)} + e^{-} \to Mg_{(g)}^{-}$

(E) $B_{(g)} + e^{-} \to B_{(g)}^{-}$ (F) $O_{(g)}^{-} + e^{-} \to O_{(g)}^{2 -}$

TestHub · Accepted Answer

The electron gain enthalpy is negative (exothermic) for Li and B. For N, Be, and Mg, the electron gain enthalpy is positive (endothermic) due to stable electron configurations or filled/half-filled subshells. The second electron gain enthalpy for O is also positive (endothermic) due to repulsion. Thus, 2 changes are exothermic.

Chemistry - PERIODIC TABLE Question with Solution | TestHub

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JEE Main 2028 (Class 11)