The following two reactions give the same foul smelling product Z.

X and Z, respectively, are :

(A) \(X= AgCN ; Z= C _2 H _5 NC\)
In the second sequence of reactions, \(C _2 H _5 CONH _2\) undergoes Hoffmann bromamide degradation with \(Br _2\) and NaOH to form a primary amine with one less carbon atom. Thus, \(Y\) is ethylamine \(\left( C _2 H _5 NH _2\right)\).
Ethylamine \((Y)\) then reacts with \(CHCl _3\) and ethanolic KOH in a carbylamine reaction to form ethyl isocyanide ( \(C _2 H _5 NC\) ), which is known for its foul smell. Therefore, \(Z\) is \(C _2 H _5 NC\).
In the first reaction, ethyl chloride \(\left( C _2 H _5 Cl \right)\) reacts with a reagent \(X\) to give the same product \(Z\left( C _2 H _5 NC \right)\). To obtain an isocyanide as the major product from an alkyl halide, the reagent used is silver cyanide \(( AgCN )\), because AgCN is predominantly covalent and the nitrogen atom acts as the nucleophilic center.
Hence, \(X= AgCN\) and \(Z= C _2 H _5 NC\).