Aldehydes can be oxidised by

The dipole moment is the highest for

The semicarbazone of cyclobutanone is represented as:

Identify the correct option regarding the distinction between pairs of compounds.

Two aliphatic aldehydes $P$ and $Q$ react in the presence of aqueous $K_2CO_3$ to give compound $R$,which upon treatment with $HCN$ provides compound $S$. On acidification and heating,$S$ gives the product shown below:
$1.$ The compounds $P$ and $Q$ respectively are:
$2.$ The compound $R$ is:
$3.$ The compound $S$ is:
Give the answer for questions $1$,$2$ and $3$.

Clemmensen reduction involves the conversion of $ >C=O $ to $ >CH_2 $ in the presence of: