Electron affinity is the

Knowing the electron gain enthalpy values for $O \rightarrow O^{-}$ and $O \rightarrow O^{2-}$ as $-141 \ kJ \ mol^{-1}$ and $702 \ kJ \ mol^{-1}$ respectively,how can you account for the formation of a large number of oxides having $O^{2-}$ species and not $O^{-}$?
(Hint: Consider lattice energy factor in the formation of compounds).

The set containing the elements with positive electron gain enthalpies is

The increasing order of electron affinity for the given electronic configurations of elements is:
$I. 1s^2 2s^2 2p^6 3s^2 3p^5$
$II. 1s^2 2s^2 2p^3$
$III. 1s^2 2s^2 2p^5$
$IV. 1s^2 2s^2 2p^6 3s^1$

The electron affinity of chlorine is $3.7 \ eV$. $1 \ g$ of chlorine is completely converted to $Cl^-$ ion in a gaseous state. $(1 \ eV = 23.06 \ kcal \ mol^{-1})$. Energy released in the process is $...... \ kcal$.

The difference between electron gain enthalpies will be maximum between: