Which one of the following species is diamagnetic in nature?

A species is diamagnetic if all its electrons are paired. We use Molecular Orbital (MO) theory to check:${\text{He}}_2^{+}$: Total electrons $=3$. Configuration: ${\sigma }_{1s}^2{\sigma }_{1s}^{\ast 1}$. It has one unpaired electron (Paramagnetic).${\text{H}}_2$: Total electrons $=2$. Configuration: ${\sigma }_{1s}^2$. All electrons are paired (Diamagnetic).${\text{H}}_2^{+}$: Total electrons $=1$. Configuration: ${\sigma }_{1s}^1$. It has one unpaired electron (Paramagnetic).${\text{H}}_2^{-}$: Total electrons $=3$. Configuration: ${\sigma }_{1s}^2{\sigma }_{1s}^{\ast 1}$. It has one unpaired electron (Paramagnetic).