Which of the following compounds reacts with ammonia to form urotropine?

Which of the following is least reactive towards nucleophilic addition?

The major product formed in the following reaction is:

Identify the reaction in which the carbonyl group of aldehydes and ketones is reduced to a methylene group upon treatment with hydrazine followed by heating with sodium hydroxide in ethylene glycol.

The structure of $(R)$ is:

Identify the final product in the following reaction sequence: $R-CHO$ $\xrightarrow{HS-(CH_2)_3-SH}$ $\xrightarrow{n-BuLi}$ $\xrightarrow{D_2O}$ $\xrightarrow{HgCl_2/CdCO_3, H_2O} \text{Product}$