Which is the best oxidizing agent to oxidize $CH_3CH=CHCHO$ to $CH_3CH=CHCOOH$?

What is reactant $A$?

The final product $(C)$ in the given reaction sequence is
$C_6H_5COOH$ $\xrightarrow{SOCl_2} (A)$ $\xrightarrow[\text{anhy. } AlCl_3]{C_6H_6} (B)$ $\xrightarrow[\text{(ii) } KOH / (CH_2OH)_2]{\text{(i) } NH_2-NH_2} (C)$

The increasing order of the equilibrium constant for the formation of a hydrate from the following compounds is:

Acetaldehyde forms a white crystalline precipitate on mixing with a ...... solution of

The major product of the following reaction sequence is