JEE Advanced 2020 — Paper 2 — Question 23

Diamagnetic (all electrons paired) are repelled i.e. magnetized in opposite direction in magnetic field, so such

substance are deflected upwards in magnetic field. Diamagnetic substances are

$$\mathrm{H}_{2} \mathrm{O}(\ell), \mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right], \mathrm{C}_{6} \mathrm{H}_{6}(\ell)$$

Paramagnetic substances (at least one unpaired electron) are attracted in magnetic field, so such substances

are deflected downwards.

$$\mathrm{O}_{2}(\mathrm{~g}): \sigma_{1 \mathrm{~s}^{2}} \sigma_{1 \mathrm{~s}^{2}}^{*} \sigma_{2 \mathrm{~s}^{2}} \sigma_{2 p_{z}^{2}} \pi_{2 p_{x}^{2}}=\pi_{2 p_{y}^{2}} \pi_{2 p_{x}^{1}}^{*}=\pi_{2 p_{y}^{1}}^{*}$$

Since $\mathrm{O}_{2}$ molecules has two unpaired electrons in antibonding $\pi$. MO.

So, $\mathrm{O}_{2}$ is paramagnetic.