Question

Which of the following compounds is expected to be coloured? (Atomic numbers are given as: $[Ag=47,Cu=29,Mg=12]$)

• A. $A{g}_{2}S{O}_4$
• B. $Cu{F}_2$
• C. $Mg{F}_2$
• D. $CuCl$

Answer 1

The correct option is B $Cu{F}_2$

The compounds of transition metals show colours mainly due to electronic transitions between partially filled d-orbitals.
a) In $A{g}_{2}S{O}_4,Ag$ is in +1 oxidation state.
The electronic configuration of $A{g}^{+1}=\left[Kr\right]4d^{10}$
So no partially filled d-orbital, so it will not show colour.
b) Here $Cu$, is in +2 oxidation state.
So the electronic configuration of
$C{u}^{+2}=\left[Ar\right]3d^9$
So this compound will show colour.
c) $Mg$ is a s-block metal. It has no d-orbital so no spliting of orbital takes place. Moreover the excited electrons have higher energy thus the emitted radiation do not fall in the visible region.
d) Here $Cu$ is in +1 oxidation state.
So the electronic configuration of
$C{u}^{+1}=\left[Ar\right]4d^{10}$
So d-orbital is completely filled, hence it will also not show colour.