Which compound has the highest value of $pK_a$?

Consider the following sequence of reactions:
$2\text{-benzylbenzoic acid}$ $\xrightarrow{SOCl_2} A$ $\xrightarrow[2. H_3O^+]{1. AlCl_3} B$ $\xrightarrow{Zn-Hg, \text{conc. } HCl, \text{heat}} C$
The end product $(C)$ is:

Concentrated nitric acid oxidises cane sugar to

Identify $C$ in the following sequence of reactions:
$2\text{-methylcyclohexanecarboxylic acid}$ $\xrightarrow{SOCl_2} A$ $\xrightarrow{NH_3} B$ $\xrightarrow{P_4O_{10}, \text{heat}} C(C_8H_{13}N)$

Arrange the following in the increasing order of their acidic strength: $CH_{3}COOH, CH_{2}ClCOOH, CHCl_{2}COOH, CCl_{3}COOH$.

Acetic acid reacts with $PCl_5$ to form