In which of the following compounds, the oxidation number of the started transition metal is zero.

Options

A. `[Fe(H_(2)O)_(3)](OH_(2))`
B. `[Co(NH_(3))_(6)]Cl_(2)`
C. `[Ni(CO_(4))]`
D. `[Pt(C_(2)H_(4))Cl_(3)]`

Answer

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

### Step 1: Analyze each compound

1. **Fe(H2O)3(OH)2**
- Assign oxidation states:
- H2O: 0 (neutral)
- OH: -1 (each OH contributes -1, and there are 2 OH groups, so total = -2)
- Let the oxidation state of Fe be \( x \).
- The equation becomes:
\[ x + 0 + (-2) = 0 \]
\[ x - 2 = 0 \implies x = +2 \]
- **Conclusion**: The oxidation state of Fe is +2.

2. **Co(NH3)6Cl2**
- Assign oxidation states:
- NH3: 0 (neutral)
- Cl: -1 (each Cl contributes -1, and there are 2 Cl, so total = -2)
- Let the oxidation state of Co be \( x \).
- The equation becomes:
\[ x + 0 + (-2) = 0 \]
\[ x - 2 = 0 \implies x = +2 \]
- **Conclusion**: The oxidation state of Co is +2.

3. **Ni(CO)4**
- Assign oxidation states:
- CO: 0 (neutral, CO is a neutral ligand)
- Let the oxidation state of Ni be \( x \).
- The equation becomes:
\[ x + 0 = 0 \]
\[ x = 0 \]
- **Conclusion**: The oxidation state of Ni is 0.

4. **Pt(C2H4)Cl3**
- Assign oxidation states:
- C2H4: 0 (neutral)
- Cl: -1 (each Cl contributes -1, and there are 3 Cl, so total = -3)
- Let the oxidation state of Pt be \( x \).
- The equation becomes:
\[ x + 0 + (-3) = 0 \]
\[ x - 3 = 0 \implies x = +3 \]
- **Conclusion**: The oxidation state of Pt is +3.

### Final Answer:
The only compound where the oxidation number of the transition metal is zero is **Ni(CO)4**.

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