According to molecular orbital theory, which of the following molecule will not be available?

• Correct answer
  A

  ${\mathrm{H}}_2^{2-}$
• B

  ${\mathrm{He}}_2^{2+}$
• C

  ${\mathrm{He}}_2^{+}$
• D

  ${\mathrm{H}}_2^{-}$

Solution

The electronic configuration of ${\mathrm{H}}_2^{2\ominus }$ is $\Rightarrow \left(\mathrm{\sigma }1{\mathrm{s}}^2\right),\mathrm{ }{\left({\mathrm{\sigma }}^{\mathrm{*}}1\mathrm{s}\right)}^2$



Bond order of ${\mathrm{H}}_2^{2⊝}=\frac{{\mathrm{N}}_{\mathrm{b}}-{\mathrm{N}}_{\mathrm{a}}}{2}=\frac{2-2}{2}=0$

Hence, ${\mathrm{H}}_2^{2\ominus }$ does not exist, due to zero bond order.

Hence, the correct answer is option: 'A'.