Question

Which of the following statement is incorrect according to crystal field theory?

• A. The $N{i}^{2+}\left(aq\right)$ cation is coloured because $N{i}^{2+}$ ion can absorb light, which promotes electrons from the low energy d-orbitals to high energy d-orbitals.
• B. The $Z{n}^{2+}\left(aq\right)$ cation is colourless because the d-orbitals are completely filled and no electrons can be promoted, so on light is absorbed.
• C. A complex which has just one absorption band at $455nm$, must be blue coloured.
• D. A complex which has just one absorption band at $425nm$, must be yellow coloured.

Answer 1

The correct option is C A complex which has just one absorption band at $455nm$, must be blue coloured.

$N{i}^{2+}$ ion is coloured because it has unpaired electrons.
$Z{n}^{2+}$ ion is colourless because it lacks unpaired electrons.
Complementary colour of the wavelength is observed for a complex.

Wavelength $425nm$ corresponds to violet colour. Thus, its complement colour is yellow. Hence, compound appears as yellow colour.

The wavelength $455nm$ corresponds to blue light. When a complex absorbs blue light, the colour observed is orange.
Thus, the complex appears orange. So, the statement in option $C$ is incorrect.


Hence, the correct option is $C$.