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: Understanding the Concept
A complex is neutral when the sum of the charge on the metal and the charges on the ligands equals zero, and no counter-ion is needed.

Step 2: Check option (A)
\(\text{K}_3[\text{Fe(CN)}_5\text{NO}]\) is a salt. The complex ion inside the bracket carries a charge of \(3-\), balanced by three \(\text{K}^+\). So the complex ion is not neutral.

Step 3: Check option (B)
\([\text{Zn(NH}_3)_4]^{2+}\) has \(\text{NH}_3\) neutral and \(\text{Zn}^{2+}\), so the overall charge is \(+2\).

Step 4: Check option (C)
\([\text{Co(NH}_3)_5\text{Cl}]^{2+}\): \(\text{Co}^{3+}\) plus \(\text{Cl}^-\) gives \(+2\).

Step 5: Check option (D)
\([\text{Ni(CO)}_4]\): carbon monoxide is neutral and nickel is in the zero oxidation state, so the complex has no charge. It is neutral.

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