In which of the following the oxidation number of metal ion is zero?

Options

A. `Ni(CO)_(4)`
B. `Fe_(2)(CO)_(9)`
C. `Na[Co(CO)_(4))]`
D. `Cu`

Answer

To determine the oxidation number of the metal ion in each of the given compounds, we will analyze each option step by step.

### Step 1: Analyze Nickel Carbonyl (Ni(CO)4)
- **Compound**: Ni(CO)4
- **Ligand**: CO (carbon monoxide) is a neutral ligand, which means it has an oxidation state of 0.
- **Oxidation State Calculation**:
- Let the oxidation state of nickel (Ni) be \( x \).
- The equation can be set up as:
\[ x + 0 = 0 \]
- Solving for \( x \):
\[ x = 0 \]
- **Conclusion**: The oxidation number of nickel in Ni(CO)4 is 0.

### Step 2: Analyze Iron Nonacarbonyl (Fe(CO)9)
- **Compound**: Fe(CO)9
- **Ligand**: CO is a neutral ligand, so its oxidation state is 0.
- **Oxidation State Calculation**:
- Let the oxidation state of iron (Fe) be \( x \).
- The equation can be set up as:
\[ x + 0 = 0 \]
- Solving for \( x \):
\[ x = 0 \]
- **Conclusion**: The oxidation number of iron in Fe(CO)9 is 0.

### Step 3: Analyze Sodium Carbonyl (Na2(CO)4)
- **Compound**: Na2(CO)4
- **Ligand**: CO is a neutral ligand, so its oxidation state is 0.
- **Oxidation State Calculation**:
- Let the oxidation state of sodium (Na) be \( x \).
- Sodium typically has an oxidation state of +1. However, we need to consider the overall charge:
\[ 2(+1) + 0 = 0 \]
- This means the overall oxidation state of the sodium ions does not affect the oxidation state of the carbonyl ligands.
- **Conclusion**: The oxidation number of sodium in Na2(CO)4 is not 0, but the carbonyl ligands are neutral.

### Step 4: Analyze Copper(II) Carbonyl (Cu(CO)2)
- **Compound**: Cu(CO)2
- **Ligand**: CO is a neutral ligand, so its oxidation state is 0.
- **Oxidation State Calculation**:
- Let the oxidation state of copper (Cu) be \( x \).
- The equation can be set up as:
\[ x + 0 = +2 \]
- Solving for \( x \):
\[ x = +2 \]
- **Conclusion**: The oxidation number of copper in Cu(CO)2 is +2.

### Final Summary of Oxidation States:
- Ni(CO)4: Oxidation state of Ni = 0
- Fe(CO)9: Oxidation state of Fe = 0
- Na2(CO)4: Oxidation state of Na = +1 (not 0)
- Cu(CO)2: Oxidation state of Cu = +2 (not 0)

### Correct Options:
The compounds where the oxidation number of the metal ion is zero are:
- Ni(CO)4
- Fe(CO)9