The oxidation number of cobalt in K[Co(CO)4] is

(i) + 1 (ii) + 3 (iii) –1 (iv) –3


K[Co(CO)4] = K + + [Co(CO)4]-

total overall charge as 0:


X + 4(0) = -1


X = -1.


Option (iii) is correct.


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