Polar molecular solids are formed by molecules that have polar covalent bonds and possess a net dipole moment. A net dipole moment arises when there is an asymmetric distribution of charge in the molecule, resulting in a separation of positive and negative charges.

Out of the given options, only option C consists of two polar molecular solids - $\mathrm{SO}_2(\mathrm{s})$ and $\mathrm{NH}_3(\mathrm{s})$. $\mathrm{SO}_2$ has polar covalent bonds due to the difference in electronegativity between sulfur and oxygen, and the molecule has a net dipole moment due to its bent molecular geometry. Similarly, $\mathrm{NH}_3$ has polar covalent bonds due to the difference in electronegativity between nitrogen and hydrogen, and the molecule has a net dipole moment due to its trigonal pyramidal molecular geometry.

Therefore, the correct answer is - $\mathrm{SO}_{2}(\mathrm{s}), \mathrm{NH}_{3}(\mathrm{s})$.