JEE Main · 2013 · 07 Apr 2013 · Offline · Chemical Bonding and Molecular Structure

A species survives only if its bond order exceeds zero. For $\mathrm{H}{}_2{}^{2+}$ both electrons have been stripped from the bonding ${\sigma }_{1s}$, leaving nothing to bond with and a bond order of $0$. For $\mathrm{He}{}_2$ the four electrons fill $({\sigma }_{1s}{)}^2({\sigma }_{1s}^{\ast }{)}^2$, so bonding and antibonding cancel and the bond order is again $0$. Both having zero bond order, neither is expected to exist.