QJEEM18Ch83c8: JEE Main 2018 Chemistry - Class 11 JEEM18Ch83c8 Solution: According to molecular orbital theory, which of the following…

Note :

According to molecules orbital theory, when a molecule have bond order = 0 then that molecule does not exist.

(a) $\,\,\,$ Configuration of $He_2^{2 + }$ (2 electrons) is = ${\sigma _{1{s^2}}}$

$\therefore\,\,\,$ Bond order = ${1 \over 2}$ (2 $-$ 0) = 1

(b) $\,\,\,$ Configuration of $He_2^ +$ (3 electrons) is = ${\sigma _{1{s^2}}}$ $\sigma _{1{s^1}}^ *$

$\therefore\,\,\,$ Bond order = ${1 \over 2}$ (2 $-$ 1) = 0.5

(c) $\,\,\,$ Configuration of $H_2^ -$ (3 electrons) is = ${\sigma _{1{s^2}}}$ $\sigma _{1{s^1}}^ *$

$\therefore$ Bond order = ${1 \over 2}$ (2 $-$ 1) = 0.5

(d) $\therefore\,\,\,$ Configuration of $He_2^{2 - }$ is = ${\sigma _{1{s^2}}}\,\,\sigma _{1{s^2}}^ *$

$\therefore\,\,\,$ Bond order = $= {1 \over 2}$ (2 $-$ 2) = 0

$\therefore\,\,\,$ $H_2^{2 - }$ is not a viable molecule.