# Which of the species is diamagnetic ?

$(a)\;O_2^{+} \\ (b)\;O_2 \\(c)\;O^-_2 \\(d)\;O_2^{2-}$

Molecular orbital configuration of $O_2^{2-}$ is
$\sigma_1 s^2 \quad \sigma ^*_1s^2 \quad \sigma _2s^2 \quad \sigma_2^* s^2 \quad \sigma_2 p_z^2 \quad \pi _2 p_x^2 \quad \pi_2 p_y^2 \quad \pi ^* _2 p_x^2 \quad \pi^* _2 p_y^2$
Due to the absence of unpaired electron, it is diamagnetic.
Hence c is the correct answer.