Which of the following species has unpaired electrons?

Solution :
$$O_2^ - :\left( {\sigma 1{s^2}} \right)\left( {{\sigma ^ * }1{s^2}} \right)\left( {\sigma 2{s^2}} \right)$$     $$\left( {{\sigma ^ * }2{s^2}} \right)\left( {\sigma 2p_z^2} \right)\left( {\pi 2p_x^2 = \pi 2p_y^2} \right)$$      $$\left( {{\pi ^ * }2p_x^2 = {\pi ^ * }2p_y^1} \right)$$
$${N_2},{F_2}$$  and $$O_2^{2 - }$$  have paired electrons.