Identify the reaction shown below:
$C_6H_5OH + CH_2O \xrightarrow{\text{acid or base}} \text{o-hydroxybenzyl alcohol} + \text{p-hydroxybenzyl alcohol}$

Identify the missing reagent in the following reaction:

Give the conversion of phenol to salicylic acid.

Some compounds and their $pK_a$ values are given. Arrange them in decreasing order of their acidic strength.
$(i)$ Ethanol $(15.9)$,Phenol $(10.0)$,Cresol $(10.1)$,Water $(15.7)$
$(ii)$ $o$-Nitrophenol $(7.2)$,$m$-Nitrophenol $(8.3)$,Ethanol $(15.9)$,Water $(15.7)$,Phenol $(10.0)$

The order of melting point of ortho-,meta-,and para-nitrophenol is

Which of the following compounds is the most acidic?