Oxygen molecule is paramagnetic in nature. What is the paramagnetic content in terms of magnetic moment $$\left( {B.M.} \right)$$  in $$O_2^ - ?$$

Solution :
$$O_2^ - :\left( {\sigma 1{s^2}} \right)\left( {{\sigma ^ * }1{s^2}} \right)\left( {\sigma 2{s^2}} \right)$$     $$\left( {{\sigma ^ * }2{s^2}} \right)\left( {\sigma 2p_z^2} \right)\left( {\pi 2p_x^2 = \pi 2p_y^2} \right)$$      $$\left( {{\pi ^ * }2p_x^2 = {\pi ^ * }2p_y^1} \right)$$
$$O_2^ - \,{\text{has 1 unpaired electron}}{\text{.}}$$
$$\mu = \sqrt {n\left( {n + 2} \right)} \,B.M. = $$       $$\sqrt {1\left( {1 + 2} \right)} = \sqrt 3 = 1.732\,B.M.$$