Answer:
See explanation
Explanation:
From the analysis we have in the question, we must look towards a first row transition metal ion having a d^6 configuration because it yields a paramagnetic complex having four unpaired electrons and a diamagnetic complex having no unpaired electrons.
We have two possible candidates in mind, Fe^2+ and Co^3+. However, Fe^2+ does not form as many coloured complexes as stated in the question so we have to eliminate that option.
We are now left with only Co^3+. Various ligands are going to cause these various colours of Co^3+ to appear in solution.
Hence, we can deduce from all these that the nature of ligands determines the colour of the complex . Don't forget that the colour of a complex arises from crystal field splitting.