For oxygen, the first electron gain enthalpy is $- 141 kJ mo l^{- 1}$ and the second is $+ 744 kJ mo l^{- 1}$ . The enthalpy change for $O (g) + 2 e^{-} \to O X^{2 -} (g)$ is

A $+ 885 kJ mo l^{- 1}$
B $- 885 kJ mo l^{- 1}$
C $- 603 kJ mo l^{- 1}$
D $+ 603 kJ mo l^{- 1}$

Answer: D

The two steps add: -141 + 744 = +603 kJ per mole. The net process is endothermic; oxide ions exist in solids only because the lattice energy released compensates for this.

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For oxygen, the first electron gain enthalpy is −141 kJ mol−1 and the second is +744 kJ mol−1. The enthalpy change for O(g)+2e−→OX2−(g) is

Answer: D

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For oxygen, the first electron gain enthalpy is $- 141 kJ mo l^{- 1}$ and the second is $+ 744 kJ mo l^{- 1}$ . The enthalpy change for $O (g) + 2 e^{-} \to O X^{2 -} (g)$ is