Question

Consider Crystal field theory and state which of the following statements is incorrect?

• A. The $N{i}^{2+}\left(aq\right)$ cation is coloured because $N{i}^{2+}$ ion can absorb light, which promotes electrons from the filled d-orbitals to the higher energy half filled 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 455 nm, must be red coloured.
• D. A complex which has just one absorption band at 425 nm, must be yellow coloured.

Answer 1

Answer: (C)

A complex which has just one absorption band at 455 nm, must be red coloured.

The wavelength 455 nm 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 $C$