$CH_3CHO$ $\xrightarrow{HCN} A$ $\xrightarrow{H_3O^+} B$. The product $B$ is

Product $(D)$ will be

The product formed by the reaction of chlorine with benzaldehyde in the absence of a catalyst is

Given below are the four isomeric compounds $(P, Q, R, S)$. Identify the correct statements from below.
$A$. $Q, R$ and $S$ will give a precipitate with $2,4-DNP$.
$B$. $P$ and $Q$ will give a positive Bayer's test.
$C$. $Q$ and $R$ will give a sooty flame.
$D$. $R$ and $S$ will give a yellow precipitate with $I_2/NaOH$.
$E$. $Q$ alone will deposit silver with Tollen's reagent.
Choose the correct option.

Which one is most reactive towards nucleophilic addition reaction?

$A$ and $B$ are isomers. Identify $B$.