Which is the strongest acid? ($pK_a$ value is given in the bracket)

When formic acid is heated with conc. $H_{2}SO_{4}$,the gas evolved is

Identify the reagent used in the following reaction: $\text{Benzoic acid} \xrightarrow[\Delta]{\text{Reagent}} \text{Benzoyl chloride} + \text{Phosphorus oxychloride} + \text{Hydrogen chloride}$.

The correct order of acidic strength among the following is:

$A$ is a high molecular weight phenol and $B$ is an aromatic carboxylic acid. Which of the following would you use to separate a mixture of $A$ and $B$?

Name the end product in the following series of reactions:
$CH_3COOH$ $\xrightarrow{NH_3} A$ $\xrightarrow[P_2O_5]{\Delta} B$