H₂O₂ is:

Peroxide ion is ${\mathrm{O}}_2^{2-}$ and its molecular orbital electronic configuration is:

$\left(\sigma 1s^2\right)\left(\sigma *1s^2\right)\left(\sigma 2s^2\right)\left(\sigma *2s^2\right)\left(\sigma 2p_z^2\right)\left(\pi 2p_x^2=\pi 2p_y^2\right)\left(\pi *2p_x^2=\pi *2p_y^2\right)$

It shows that the peroxide ion is diamagnetic.

 H₂O₂ also has a peroxide ion, therefore it is also diamagnetic.