Which of the following diatomic molecules would be stabilised by...

In ${O}_{2}$, molecule, last two electrons are present in anti bonding
orbitals.
${O}_{2}\left(8 + 8 = 16\right) = \sigma1s^{2}, {σ}^{*}1s^{2}, \sigma2s^{2}, {σ}^{*}2s^{2}, \sigma2{pz}^{2}, \pi2{px}^{2} = \pi2{py}^{2}, {\pi}^{*}2{px}^{1} = {\pi}^{*}2{py}^{1}$
Removal of one electron from the ${O}_{2}$, molecule gives ${O}_{2}^{+}$ in which the number of anti bonding electrons is one less and hence, $BO$ increases. Thus, removal of one electron from ${O}_{2}$ stabilises the molecule.