The major product Z formed in the following sequence of reactions is :
\(C _2 H _6 \xrightarrow[\text { UV light }]{ Cl _2} X \xrightarrow{ NH _3} Y \xrightarrow[\text { (monochlorinated product) }]{\text { (i) } NaNO _2 / HCl \text { (ii) } H _2 O } Z\)

(C) Ethane undergoes free radical halogenation with chlorine in the presence of UV light to form ethyl chloride (X).
\(C_2 H_6+Cl_2 \xrightarrow{\text { UV light }} C_2 H_5 Cl(X) \)
Ethyl chloride reacts with ammonia via nucleophilic substitution to form ethylamine (Y).
\(C_2 H_5 Cl+NH_3 \rightarrow C_2 H_5 NH_2(Y)\)
Ethylamine, being a primary aliphatic amine, reacts with nitrous acid ( \(NaNO _2+ HCl\) ) to form an unstable aliphatic diazonium salt, which decomposes to yield a carbocation. The carbocation reacts with water to form ethanol (Z).
\(C_2 H_5 NH_2 \xrightarrow{NaNO_2 / HCl}\left[C_2 H_5 N_2^{+} Cl^{-}\right] \xrightarrow{H_2 O} C_2 H_5 OH(Z)+N_2+HCl\)
Thus, the major product Z is \(C _2 H _5 OH\).