Question

The oxidation number of cobalt in \(K[Co(CO)_4]\) is

• A. \(+1\)
• B. \(+3\)
• C. \(-1\)
• D. \(-3\)

Answer 1

The Correct Option is C

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

Answer 2

The oxidation number represents the degree of oxidation of an atom within a chemical compound. It can be a negative, positive, or zero value, and it is always an integer.
To determine the oxidation state of cobalt in K[Co(CO)4], we need to know the oxidation states of potassium and carbon monoxide. Potassium has a constant oxidation state of +1, and carbon monoxide has an oxidation state of 0. Additionally, since the compound is neutral (as there is no charge indicated in its molecular formula), the sum of the oxidation states in the compound is 0.
Let’s denote the oxidation state of cobalt as X. Therefore, the total oxidation state of the compound can be expressed as follows:
(Oxidation state of potassium)+X+4(Oxidation state of CO)
Given:
oxidation state of K=+1
Oxidation state of CO=0
Total oxidation state of the complex=0
Substituting these values into the equation, we get:
1+X+4(0)=0
1+X =0
X=-1
Therefore, the oxidation state of cobalt (X) is -1. 
Thus, the correct option is: (C).