Identify the correct statements from the following. (I) $\mathrm{SnCl}_2$ is ionic, but $\mathrm{SnCl}_4$ is covalent in nature. (II) All linear diatomic molecules have zero dipole moment. (III) Both $\mathrm{NO}$ and $\mathrm{O}_2$ are paramagnetic.

Among the given statements only I and III are correct and II is incorrect. All linear diatomic molecules does not have zero dipole moment. e.g. $\mathrm{HF}, \mathrm{HCl}, \mathrm{HBr}$ etc. Hence, statement II is incorrect. According to Fajan's rule the central metal with more oxidation state will be considerded to be more covalent molecule than that have low oxidation state. In $\mathrm{SnCl}_2$ and $\mathrm{SnCl}_4$ the oxidation state of $\mathrm{Sn}$ is +2 and +4 respectively. Thus, $\mathrm{SnCl}_4$ is more covalent. Due to the presence of one unpaired electron in $\mathrm{NO}$ and two in $\mathrm{O}_2$, both are paramagnetic in nature.