Substances that are repelled by an external magnetic field are diamagnetic (possessing zero unpaired electrons):

• In $\text{Na}_2[\text{CdCl}_4]$, cadmium is in $+2$ oxidation state: $\text{Cd}^{2+} = [\text{Kr}]4d^{10}$ (all electrons paired, diamagnetic).
• In $\text{K}_4[\text{Fe}(\text{CN})_6]$, iron is in $+2$ state: $\text{Fe}^{2+} = [\text{Ar}]3d^6$ low spin $t_{2g}^6 e_g^0$ (all electrons paired, also diamagnetic).
• In $\text{Na}_2[\text{CuCl}_4]$, $\text{Cu}^{2+} = 3d^9$ (1 unpaired electron, paramagnetic).
• In $\text{K}_3[\text{Fe}(\text{CN})_6]$, $\text{Fe}^{3+} = 3d^5$ low spin $t_{2g}^5 e_g^0$ (1 unpaired electron, paramagnetic).

NTA official answer key accepted option 2 (option 3 is also diamagnetic).