a
\(CoCl _{3} \cdot 4 NH _{3} \rightarrow\left[ Co \left( NH _{3}\right)_{4} Cl _{2}\right] Cl\)

\(NiCl _{2} \cdot 6 H _{2} O \rightarrow\left[ Ni \left( H _{2} O \right)_{6}\right] Cl _{2}\)

\(PtCl _{4} \cdot 2 HCl \rightarrow H _{2}\left[ PtCl _{6}\right]\)

\(\left[ Ni \left( H _{2} O \right)_{6}\right] Cl _{2} \stackrel{2 AgNO _{3}}{\longrightarrow} 2 AgCl \downarrow+\left[ Ni \left( H _{2} O \right)_{6}\right]\left( NO _{3}\right)_{2}\)

\(\mu=\sqrt{2(2+2)}\) B.M \(=2.84 BM \approx 3\)