Mark the correct statement from the following :

Options

A. Copper metal can be oxidised by `Zn^(2+)` ions.
B. Oxidation number of phosphorus in `P_(4)` is 4
C. An element in the highest oxidation state acts only as a reducing agent.
D. The element which shows highest oxidation number of +8 is Os in `OsO_(4)`

Explanation

To solve the question of identifying the correct statement among the given options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze Statement 1**: "Copper metal can be oxidized by Zn²⁺ ions."
- To determine the validity of this statement, we need to look at the standard reduction potentials:
- **E° (Zn²⁺/Zn)** = -0.763 V
- **E° (Cu²⁺/Cu)** = +0.337 V
- Since copper has a higher reduction potential, it means that copper is a better oxidizing agent than zinc. Therefore, zinc cannot oxidize copper; rather, zinc can reduce copper ions to copper metal.
- **Conclusion**: This statement is **incorrect**.

2. **Analyze Statement 2**: "Oxidation number of phosphorus in P₄ is 4."
- In its elemental form (P₄), phosphorus has an oxidation state of 0.
- **Conclusion**: This statement is **incorrect**.

3. **Analyze Statement 3**: "An element in the highest oxidation state acts only as a reducing agent."
- A reducing agent is one that gets oxidized while reducing another substance. An element in the highest oxidation state typically tends to gain electrons and be reduced, not oxidized. Therefore, it would act as an oxidizing agent instead.
- **Conclusion**: This statement is **incorrect**.

4. **Analyze Statement 4**: "The element which shows the highest oxidation number of +8 is Os in OsO₄."
- To find the oxidation state of osmium (Os) in OsO₄:
- Let the oxidation state of Os be X.
- The equation becomes: X + 4(-2) = 0 (since the overall charge is neutral).
- This simplifies to: X - 8 = 0 → X = +8.
- Therefore, osmium in OsO₄ indeed has an oxidation state of +8.
- **Conclusion**: This statement is **correct**.

### Final Answer:
The correct statement is **Statement 4**: "The element which shows the highest oxidation number of +8 is Os in OsO₄."

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