Question

The oxidation number of cobalt in K[Co(CO)₄] is
(i) +1
(ii) +3
(iii) −1
(iv) −3

Answer 1

We know that CO is a neutral ligand and K carries a charge of +1. Therefore, the complex can be written as K+[Co(CO)₄]−. Therefore, the oxidation number
of Co in the given complex is −1. Hence, option (iii) is correct.