The set containing the elements with positive electron gain enthalpies is

Electron gain enthalpy values $(\Delta_{eg} H)$ (in $kJ \ mol^{-1}$) of elements $X$,$Y$ and $Z$ are $-349$,$-200$ and $-295$ respectively. $X$,$Y$ and $Z$ are respectively

$Na^{-} \xleftarrow{x} Na \xrightarrow{5 \ eV} Na^{+}$
Predict the value of $X$ in $eV$.

Which will have the maximum value of electron affinity among $O^x, O^y$ and $O^z$ ($x, y$ and $z$ are $0, -1$ and $-2$ respectively)?

Identify the element having positive electron gain enthalpy.

The formation of the oxide ion $O_{(g)}^{2-}$ requires first an exothermic and then an endothermic step as shown below. This is because
$O_{(g)} + e^{-} \rightarrow O_{(g)}^{-}; \Delta H^{o} = -142 \ kJ \ mol^{-1}$
$O_{(g)}^{-} + e^{-} \rightarrow O_{(g)}^{2-}; \Delta H^{o} = 844 \ kJ \ mol^{-1}$