Question

The number of antibonding 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)

$4$

The electronic configuration of the $O_2^{2-}$ ion containing 18 electrons can be written as:
$1s^2<\underset{–}{1s^{\ast 2}}<2s^2<\underset{–}{2s^{\ast 2}}<2p_z^2<(2p_x^2=2p_y^2)<(\underset{–}{2p_x^{\ast 2}}=\underset{–}{2p_y^{\ast 2}})<2p_z^{\ast 0}$
So the number of antibonding electron pairs is $4$.