Given below are two statements. One is labelled as Assertion A and...

Ionization energy of oxygen is less than that of nitrogen because $2p$ subshell of nitrogen is half filled, and half filled orbitals have some extra stability, so removing electrons from them will be little more difficult.
And In oxygen atom, $2$ of the $four2p$ electrons must occupy the same $2p$ orbital resulting in an increased electron electron-repulsion.

$N = 1{s}^{2}2{s}^{2}2{p}^{3}$

$O = 1{s}^{2}2{s}^{2}2{p}^{4}$