Question

Which of the following ions is colourless ?

• A. $Cu^+$
• B. $CO^{2+}$
• C. $Ni^{2+}$
• D. $Fe^{3+}$

Answer 1

Answer: (A)

$Cu^+$

Answer 2

$Cu^{2+} : [Ar]^{18}\, 3d^{10}$ $Ni^{2+} : [Ar]^{18} \, 3d^8$ $Co^{2+} : [Ar]^{18} \, 3d^7$ $Fe^{2+} : [Ar]^{18} \, 3d^6$ $Cu^+$ with no unpaired electron is white or colourless