Question

Oxidation number of cobalt in K[Co(CO)$_4$] is

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

Hint:

When finding oxidation numbers in coordination compounds, remember: neutral ligands like CO, NH$_3$, and H$_2$O contribute zero charge, while ionic ligands like Cl$^-$ or OH$^-$ contribute their usual charge.

Answer 1

The Correct Option is A

To calculate the oxidation number of cobalt in the given complex \( K[Co(CO)_4] \):

Step 1: Assign charges of known species.
- Potassium (K) has an oxidation state of \( +1 \).
- Carbonyl (CO) is a neutral ligand, so each CO contributes \( 0 \) charge.

Step 2: Write the overall charge balance equation.
Let the oxidation number of cobalt be \( x \). The complex ion is \([Co(CO)_4]^-\), since K is outside with \( +1 \).
\[ x + (4 \times 0) = -1 \]

Step 3: Solve for \( x \).
\[ x = -1 \] Thus, the oxidation number of cobalt in \( K[Co(CO)_4] \) is \( -1 \).