\(Cu ^{2+}\) form \(\left[ Cu \left( H _{2} O \right)_{4}\right]^{2+}\) complex ion with \(H _{2} O.\)

\(\left[ Cu \left( H _{2} O \right)_{4}\right]^{2+} \Rightarrow Cu ^{2+}[ Ar ] 3 d ^{9}, H _{2} O \rightarrow WFL\)

number of unpaired \(e ^{-}=1\)

\(\mu=\sqrt{1(1+2)}\) \(B.M.\)

\(\mu=\sqrt{3} \Rightarrow 1.73 \,B.M . \Rightarrow \text { round off ans. } \Rightarrow 2\)