Which of the following reactions converts the carbonyl group of aldehydes and ketones to a methylene group on treatment with zinc amalgam and concentrated $HCl$?

Which of the following is Clemmensen reduction?

The product formed in the reaction is:

In the presence of a dilute base,$C_6H_5CHO$ and $CH_3CHO$ react together to give a product. The product is

An optically active alkyl bromide $C_4H_9Br$ reacts with ethanolic $KOH$ to form major compound $[A]$, which reacts with bromine to give compound $[B]$. Compound $[B]$ reacts with ethanolic $KOH$ and sodamide to give compound $[C]$. One molecule of water adds to compound $[C]$ on warming with mercuric sulphate and dilute sulphuric acid at $333 \text{ K}$ to form compound $[D]$. The functional group in compound $[D]$ will be confirmed by:

$(C_2H_5O)_2CO \xrightarrow[H_3O^{+}]{CH_3MgBr(\text{excess})} A$. $A$ (alcohol) can also be obtained by: