Which of the following statements about colour and absorption are correct?

A $[Cr (NH X_{3}) X_{6}] X^{3 +}$ absorbs light of shorter wavelength than $[Cr (H X_{2} O) X_{6}] X^{3 +}$ .
B $[Co (CN) X_{6}] X^{3 -}$ absorbs light of longer wavelength than $[CoF X_{6}] X^{3 -}$ .
C $[Zn (H X_{2} O) X_{6}] X^{2 +}$ is colourless because a $d^{10}$ ion has no d-d transition.
D $[Sc (H X_{2} O) X_{6}] X^{3 +}$ is coloured because of d-d transitions.

Answer: A, C

Ammonia gives a larger

Δ_{o}

than water, so absorption is at higher energy, i.e. shorter wavelength (statement 1 true). Cyanide gives a larger

Δ_{o}

than fluoride, so

[Co (CN) X_{6}] X^{3 -}

absorbs at shorter wavelength (statement 2 false).

d^{10}

and

d^{0}

ions have no d-d transition, so

Zn X^{2 +}

(true) and

Sc X^{3 +}

(statement 4 false) are colourless.