Question

Which of the following complex is neutral?

• A. \(\text{K}_3[\text{Fe(CN)}_5\text{NO}]\)
• B. \([\text{Zn(NH}_3)_4]^{2+}\)
• C. \([\text{Co(NH}_3)_5\text{Cl}]^{2+}\)
• D. \([\text{Ni(CO)}_4]\)

Hint:

A complex is neutral when the oxidation state of the metal cancels the charge of the ligands.

Answer 1

The Correct Option is D

Step 1: Approach
Work out the charge on each complex species by adding the charges on the metal and on the ligands.

Step 2: Counting
- (A) Three $\text{K}^+$ outside means the bracket has charge $-3$.
- (B) $+2$ (written on the formula).
- (C) $+2$ (written on the formula).
- (D) No charge written. Ligand CO is neutral, so Ni is $0$ and the molecule is neutral.

Step 3: Conclusion
Only option (D) has zero net charge, so it is the neutral complex.

Final Answer:
$[\text{Ni(CO)}_4]$ has a neutral ligand and nickel in the zero state, so it is neutral, option (D). \[ \boxed{[\text{Ni(CO)}_4]} \]