Question

why do transition metal form coloured ​

Answer 1

Explanation:

The reason why transition metal in particular are colorful is because they have unfilled or either half filled d orbitals. There is Crystal field theory which explains the splitting of the d orbital, which splits the d orbital to a higher and lower orbital. Now, the electrons of the transition metal can "jump".

Answer 2

When light falls on the transition element compounds electrons excite and electrons absorb energy and excite.

When these electrons de-excite they release visible light wavelength.