Which of the following is reduced by $Zn-Hg/HCl$ to give the corresponding hydrocarbon?

Compound $(A)$ with molecular formula $C_6H_{12}O$ is optically active. Compound $(A)$ gives a negative Tollens test and a positive test with $2,4$-dinitrophenylhydrazine. Identify $(A)$.

What is the main product obtained by the cross-aldol condensation of benzene carbaldehyde and $1$-phenyl ethane$-1$-one?

Paraldehyde is a trimer of which of the following?

The product formed in the reaction is:

Identify the reaction in which the carbonyl group of aldehydes and ketones is reduced to a methylene group upon treatment with zinc-amalgam and concentrated hydrochloric acid.