Which one has maximum electron affinity?

Which of the following transformations requires the least amount of energy?

The least stable ion is

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

$A = 1s^2\, 2s^2\, 2p^4$,$B = 1s^2\, 2s^2\, 2p^5$,$C = 1s^2\, 2s^2\, 2p^6$. $A, B$ and $C$ are atoms/anions of the same element. Which one is correct? (One of $A/B/C$ is a neutral atom)

What is the value of electron gain enthalpy of $Na^{+}$ if $IE_{1}$ of $Na$ is $5.1 \ eV$? .......... $eV$