Which reaction is used to make salicylic acid from phenol?

By passing vapours of phenol over heated $zinc$ dust will produce :

Which of the following compounds has the lowest boiling point?

Which among the following has the highest melting point?

One mole of phenol is treated with dilute $HNO_3$ at $298 \ K$ to give a mixture of products. The mixture is separated by steam distillation. The steam volatile compound $(X)$ is separated. The increase in percentage of oxygen in $(X)$ with respect to phenol is . . . . . . $\times 10^{-1}$ %. (Given molar mass in $g \ mol^{-1}$: $H:1, C:12, N:14, O:16$)

What is the correct order of increasing dissociation constant $(K_a)$ for the following compounds?