[orgoclear]

A few Cu(I) salts are coloured. The colour arises from
(a) d-d transition
(b) Charge transfer spectra
(c) The large wavelengths of the rays absorbed by the solutions
(d) the smaller wavelengths of the rays absorbed by the solutions

[Arctic-Nation]

You should indicate whether you're talking about solution or solid phase, as while most copper(I) solutions are blue, a quick search on wikipedia taught me that the salts can vary from greenish blue to red.

In the case of solutions, however, it's a simple matter of elimination. Cu(I) has a closed d shell, so option (a) is out. Charge transfer seems unlikely in the absence of suitable ligands (someone correct me if I'm mistaken here), so in the end the only option is (c), with long wavelengths (red light) being absorbed, giving blue solutions.

[orgoclear]

I typed the question provided...
strangely the answer was given to be (b) charge transfer spectra...

Searching my ino. chm book (JD LEE)

it has also written albeit not explained . that it is due to charge transfer..

I wonder how charge transfer is possible here