Question

The oxidation number of cobalt in $\mathrm{K}\left[\mathrm{Co}{\left(\mathrm{CO}\right)}_4\right]$ is

• A. $+1$
• B. $+3$
• C. $-1$
• D. $-3$

Answer 1

The correct option is C

$-1$

Explanation for correct option

(C)$-1$

Oxidation number

• "Oxidation number denotes the oxidation state of an element in a compound ascertained according to a set of rules formulated on the basis that electron pair in a covalent bond belongs entirely to a more electronegative element."

Oxidation number of cobalt in $\mathrm{K}\left[\mathrm{Co}{\left(\mathrm{CO}\right)}_4\right]$

• Consider the oxidation number of cobalt$\left(\mathrm{Co}\right)$ is $x$.
• Here, carbon monoxide is present as ligand. It is a neutral ligand. So, the oxidation number of $\mathrm{CO}$ is $0$.
• The oxidation number of potassium is $+1$.

$$\begin{gathered} +1+x+4\times 0=0 \\ x=-1 \end{gathered}$$

Explanation for incorrect option

The oxidation number of cobalt in $\mathrm{K}\left[\mathrm{Co}{\left(\mathrm{CO}\right)}_4\right]$ is $-1$. Hence, options (A), (B), and (D) are incorrect.

Hence, option (C) is correct. The oxidation number of cobalt in $\mathrm{K}\left[\mathrm{Co}{\left(\mathrm{CO}\right)}_4\right]$ is $-1$.