A certain first-row transition metal ion forms many different colored solutions. When four coordination compounds of this metal, each having the same coordination number, are dissolved in water, the colors of the solutions are red, yellow, green, and blue. Further experiments reveal that two of the complex ions are paramagnetic with four unpaired electrons and the other two are diamagnetic. What can be deduced from this information about the four coordination compounds

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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.

the answer would be b i believe