Identify B and C and how are A and C related?

Identify the correct set of reagents or reaction conditions '$$X$$' and '$$Y$$' in the following set of transformation.

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 $\mathrm{AgCN}$ form isocyanide as the main product.

Reason (R) : $\mathrm{KCN}$ and $\mathrm{AgCN}$ both are highly ionic compounds.

In the light of the above statements, choose the most appropriate answer from the options given below :

Identify A and B in the following reaction sequence.