The compound $A$ (major product) is

Assertion $(A)$: $1-$Bromopentane reacts with $AgCN$ to give pentylisocyanide.
Reason $(R)$: $AgCN$ is mainly ionic in nature.

$A$ dihalogen derivative $X$ of a three-carbon hydrocarbon reacts with alcoholic $KOH$ to give another hydrocarbon,which gives a red precipitate with ammoniacal $Cu_2Cl_2$. Reaction of $X$ with aqueous $KOH$ gives an aldehyde. The compound $X$ is .......

If all the nucleophilic substitution reactions at saturated carbon atoms in the above sequence of reactions follow $S_N2$ mechanism, then $\underline{E}$ and $\underline{E}$ will be respectively,

Polysubstitution is a major drawback in

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$ : Haloalkanes react with $KCN$ to form alkyl cyanides as a main product while with $AgCN$ they form isocyanide as the main product.
Reason $(R)$ : $KCN$ and $AgCN$ both are highly ionic compounds.
In the light of the above statement,choose the most appropriate answer from the options given below: