Arrange the following compounds in the increasing order of their $pK_a$ values:
$I.$ Phenol
$II.$ $p$-Nitrophenol
$III.$ Ethanol
$IV.$ $p$-Nitrobenzoic acid

Hydrolysis of an ester gives a carboxylic acid,which upon Kolbe's electrolysis yields ethane. Identify the ester.

Considering the reaction sequence given below,the correct statement$(s)$ is(are):
$A$. $P$ can be reduced to a primary alcohol using $NaBH_4$.
$B$. Treating $P$ with conc. $NH_4OH$ solution followed by acidification gives $Q$.
$C$. Treating $Q$ with a solution of $NaNO_2$ in aq. $HCl$ liberates $N_2$.
$D$. $P$ is more acidic than $CH_3CH_2COOH$.

The end product of the above reaction is:

Ester and acetamide are distinguished by

In the given reaction,reagents '$X$' and '$Y$' respectively are: