Which of the following compounds exhibits Schiff test?

Which of the following reactions is preferentially used to prepare the corresponding paraffins from alkanone?

Identify the reason for the highest boiling point of R-COOH as compared to alkanes, ethers, alcohols and aldehydes.

Aniline on treatment with $\text{NaNO}_2$ / HCl at about $0^\circ\text{C}$ gives a compound A, which on further treatment with CuCN / KCN gives a compound B, which when reacts with $\text{H}_2$ / Ni gives a compound C. The compound C on reaction with $\text{HNO}_2$ gives a compound D. The structure of D is: