Accroding to Molecular orbital theory, a molecule of H₂ has two electrons in

H₂ = Total number of electrons  = 1 + 1 = 2e^-s [≤ 14 e^-s]

σ1s² σ^*1s⁰;

$\mathrm{B}.\mathrm{O}=\frac{{\mathrm{N}}_{\mathrm{b}}-{\mathrm{N}}_{\mathrm{a}}}{2}$

$\mathrm{B}·\mathrm{O}=\frac{2-0}{2}=1$

In H₂ molecule two electrons  are present in ${\mathrm{\sigma }}_{1\mathrm{s}}$molecular orbital.