b
\(Cu ^{2+}+ NH _{3} \stackrel{ K _{1}}{\rightleftharpoons}\left[ Cu \left( NH _{3}\right)\right]^{2+}\)

\(\left[ Cu \left( NH _{3}\right)\right]^{2+}+ NH _{3} \stackrel{ K ,}{\rightleftharpoons}\left[ Cu \left( NH _{3}\right)_{2}\right]^{2+}\)

\(\left[ Cu \left( NH _{3}\right)_{2}\right]^{2+}+ NH _{3} \stackrel{ K _{3}}{\rightleftharpoons}\left[ Cu \left( NH _{3}\right)_{3}\right]^{2+}\)

\(\left[ Cu \left( NH _{3}\right)_{3}\right]^{2+}+ NH _{3} \stackrel{ K _{ a }}{\rightleftharpoons}\left[ Cu \left( NH _{3}\right)_{4}\right]^{2+}\)

\(Cu ^{2+}+4 NH _{3} \stackrel{ K }{\rightleftharpoons}\left[ Cu \left( NH _{3}\right)_{4}\right]^{2+}\)

So

\(K = K _{1} \times K _{2} \times K _{3} \times K _{4}\)

\(=10^{4} \times 1.58 \times 10^{3} \times 5 \times 10^{2} \times 10^{2}\)

\(K =7.9 \times 10^{11}\)

Where \(K \rightarrow\) Equilibrium constant for formation of \(\left[ Cu \left( NH _{3}\right)_{4}\right]^{2+}\)

So equilibrium constant \(\left( K ^{\prime}\right)\) for dissociation

of \(\left[ Cu \left( NH _{3}\right)_{4}\right]^{2+}\) is \(\frac{1}{ K }\)

\(K ^{\prime}=\frac{1}{ K }\)

\(K ^{\prime}=\frac{1}{7.9 \times 10^{11}}\)

\(=1.26 \times 10^{-12}=\left( x \times 10^{-12}\right)\)

So the value of \(x=1.26\)

\(OMR\) Ans \(=1\) (After rounded off to the nearest integer)