Identify the magnetic behavior mentioned in the statements

• Species that are attracted by a magnetic field and get magnetized in the same direction are paramagnetic.
• Species that are weakly repelled by a magnetic field and get magnetized in the opposite direction are diamagnetic.

Check Statement I

Statement I says: $\mathrm{O_2},\ \mathrm{Cu^{2+}},\ \mathrm{Fe^{3+}}$ are weakly attracted by magnetic field and are magnetized in the same direction as magnetic field.

Let us examine each species:

• $\mathrm{O_2}$: Molecular oxygen has two unpaired electrons in antibonding $\pi^*$ orbitals, so it is paramagnetic.

• $\mathrm{Cu^{2+}}$: Copper atomic number is $29$. $\mathrm{Cu} = [Ar]3d^{10}4s^1$ $\mathrm{Cu^{2+}} = [Ar]3d^9$ A $3d^9$ configuration has one unpaired electron, so it is paramagnetic.

• $\mathrm{Fe^{3+}}$: Iron atomic number is $26$. $\mathrm{Fe} = [Ar]3d^64s^2$ $\mathrm{Fe^{3+}} = [Ar]3d^5$ A $3d^5$ configuration has five unpaired electrons, so it is paramagnetic.

Since all three are paramagnetic, they are weakly attracted by magnetic field and magnetized in the same direction.

Therefore, Statement I is correct.

Check Statement II

Statement II says: $\mathrm{NaCl}$ and $\mathrm{H_2O}$ are weakly magnetized in opposite direction to magnetic field.

• $\mathrm{NaCl}$: $\mathrm{Na^+}$ has configuration $[Ne]$ and $\mathrm{Cl^-}$ has configuration $[Ar]$. Both have all electrons paired. So $\mathrm{NaCl}$ is diamagnetic.

• $\mathrm{H_2O}$: All electrons are paired in water molecule, so $\mathrm{H_2O}$ is also diamagnetic.

Diamagnetic substances are weakly magnetized in the direction opposite to the applied magnetic field.

Therefore, Statement II is correct.

Final conclusion

• Statement I: Correct
• Statement II: Correct

Hence, the correct option is A.