Question

Which of the following is a coloured compound?
(A) $Cu{F_2}$
(B) $CuI$
(C) $NaCl$
(D) $MgC{l_2}$

Answer 1

The transition metal compounds are often colored because of transition of electrons between d orbitals of different energy. The d block elements having unpaired electrons form coloured compounds.

Complete step by step solution:
When a visible light falls on a transition metal compound or ion, the unpaired electrons present in the lower energy d-orbital get promoted to higher energy d-orbital. This is called a d-d transition.
Therefore, the transmitted light shows the same color complementary to the absorbed color.
Therefore in $Cu{F_2}$
The electronic configuration of Cu is
$= 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^0}3{d^9}$
Thus, it has one unpaired electron.
So, it has one unpaired electron and hence, $Cu{F_2}$ is a coloured compound.
It is a white crystalline, hygroscopic solid with a rutile-type crystal structure.

Hence, option A is correct.

Note: Copper fluoride can be used to make fluorinated aromatic hydrocarbons by reacting with aromatic hydrocarbons in an oxygen- containing atmosphere at temperatures above ${450^ \circ }C$. This reaction is only effective in making compounds that can survive at the temperature used.