Question

Among the following, diamagnetic molecule is:

• A. Super oxide ion
• B. Oxygen molecule
• C. Carbon molecule
• D. Unipositive ion of nitrogen molecule

Answer 1

The correct option is C Carbon molecule

(a) Super oxide ion
$O_2^{-}:\left({\sigma }_{1s}{)}^2\right({\sigma }_{1s}^{\ast }{)}^2\left({\sigma }_{2s}{)}^2\right({\sigma }_{2s}^{\ast }{)}^2\left({\sigma }_{2p_z}{)}^2\right({\pi }_{2p_x}{)}^2=\left({\pi }_{2p_y}{)}^2\right({\pi }_{2p_x}^{\ast }{)}^2=\left({\pi }_{2p_y}^{\ast }{)}^1\right({\sigma }_{2p_z}^{\ast }{)}^0$
Since, unpaired electron is present in $({\pi }_{2p_y}^{\ast }{)}^1$ orbital, it is paramagnetic speices.
(b) Oxygen molecule
$O_2:\left({\sigma }_{1s}{)}^2\right({\sigma }_{1s}^{\ast }{)}^2\left({\sigma }_{2s}{)}^2\right({\sigma }_{2s}^{\ast }{)}^2\left({\sigma }_{2p_z}{)}^2\right({\pi }_{2p_x}{)}^2=\left({\pi }_{2p_y}{)}^2\right({\pi }_{2p_x}^{\ast }{)}^1=\left({\pi }_{2p_y}^{\ast }{)}^1\right({\sigma }_{2p_z}^{\ast }{)}^0$
Since, unpaired electron is present in $({\pi }_{2p_x}^{\ast }{)}^1=({\pi }_{2p_y}^{\ast }{)}^1$orbital, it is paramagnetic molecule.
(c) Carbon molecule
$C_2:\left({\sigma }_{1s}{)}^2\right({\sigma }_{1s}^{\ast }{)}^2\left({\sigma }_{2s}{)}^2\right({\sigma }_{2s}^{\ast }{)}^2({\pi }_{2p_x}{)}^2=({\pi }_{2p_y}{)}^2({\sigma }_{2p_z}{)}^0$
Since, all electrons are paired, it is a diamagnetic molecule.
(d) $N_2^{+}:\left({\sigma }_{1s}{)}^2\right({\sigma }_{1s}^{\ast }{)}^2\left({\sigma }_{2s}{)}^2\right({\sigma }_{2s}^{\ast }{)}^2({\pi }_{2p_x}{)}^2=({\pi }_{2p_y}{)}^2({\sigma }_{2p_z}{)}^1$
Since, unpaired electron is present in $({\sigma }_{2p_z}{)}^1$ orbital, it is paramagnetic speices.