Question

Which of the following is colourless?

• A. $\left[Cu\right(H_{2}O{)}_4{]}^{2+}$
• B. $\left[Cu\right(CN{)}_2{]}^{-}$
• C. $Cu(N{H}_3{)}_4{]}^{2+}$
• D. $[CuC{l}_4{]}^{2-}$

Answer 1

The correct option is B $\left[Cu\right(CN{)}_2{]}^{-}$

Cu is Cu(I) in $\left[Cu\right(CN{)}_2{]}^{-}$ and has $3d^9$ configuration. All others have Cu(II) and $3d^{10}$ configuration.