Question

The number of anitbonding electron pairs in $O_2^{2-}$ molecular ion on the basis of molecular orbital theory is:

• A. $2$
• B. $3$
• C. $4$
• D. $5$

Answer 1

Answer: (C)

$4$

Write configuration of $O_2^{2-}$ according to molecular orbital theory and count number of electron pairs in antibonding molecular orbitals.
$O_2^{2-}=8+8+2=18$
$=\sigma 1s^2,\stackrel{\ast }{\sigma }1s^2,\sigma 2s^2,\stackrel{\ast }{\sigma }2s^2,\sigma 2p_z^2,\pi 2p_x^2,\pi 2p_y^2,\stackrel{\ast }{\pi }2p_x^2,\stackrel{\ast }{\pi }2p_y^2$
$\therefore$ Antibonding electron pairs are
$\stackrel{\ast }{\sigma }1s^2,\stackrel{\ast }{\sigma }2s^2,\stackrel{\ast }{\pi }2p_x^2,\stackrel{\ast }{\pi }2p_y^2$
$\therefore$ Total $4$ antibonding electron pairs are there.