Consider the following table:
$\begin{pmatrix}Subs\tan ce & \text{Melting point/}^{o}C & Boiling\text{ point/}^{o}C & \\ P & -78 & -25 & \\ Q & -8 & 40 & \\ R & -6 & 150 & \\ S & -44 & 280 & \end{pmatrix}$


substances is a liquid at room temperature and rapidly evaporates on exposure to air?