Question

In which of the following pairs of molecules/ions both the species are not likely to exist ?

• A. $H_2^{-},H{e}_2^{2-}$
• B. $H_2^{2+},H{e}_2$
• C. $H_2^{-},H{e}_2^{2+}$
• D. $H_2^{+},H{e}_2^{2+}$

Answer 1

Answer: (B)

$H_2^{2+},H{e}_2$

For $H_2^{-}$, $1s^2\ast 1s^1$ Bond Order = $\frac{2-1}{2}=0.5$

For $H{e}_2^{-2}$, $1s^2\ast 1s^{2}2s^2$ Bond Order = $\frac{4-2}{2}=1$

For $H{e}_2$, $1s^2\ast 1s^2$ Bond Order = $\frac{2-2}{2}=0$

For $H_2^{+2}$, $1s^0$ Bond Order = $\frac{0-0}{2}=0$

For $H_2^{-}$, $1s^2\ast 1s^1$ Bond Order = $\frac{2-1}{2}=0.5$

For $H{e}_2^{+2}$, $1s^2$ Bond Order = $\frac{2-0}{2}=1$

For $H_2^{+}$, $1s^1$ Bond Order = $\frac{1-0}{2}=0.5$

The bond order of $H_2^{2+}$ and $H{e}_2$ is zero, thus their existence is not possible.

Hence, option B is correct.