Assertion :- Oxidation number of Carbon in all it's compounds is `+4`.
Reason :- An element has a fixed oxidation state.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False.

Answer

To solve the question, we need to analyze the assertion and the reason provided.

### Step 1: Analyze the Assertion
The assertion states that "the oxidation number of Carbon in all its compounds is +4."

1. **Identify Carbon Compounds**: Let's consider some common compounds of carbon:
- Carbon Dioxide (CO₂)
- Formic Acid (HCOOH)
- Methanol (HCHO)

2. **Calculate Oxidation State of Carbon**:
- In CO₂:
- Let the oxidation state of Carbon be \(X\).
- The equation is \(X + 2(-2) = 0\) (since each Oxygen has an oxidation state of -2).
- Solving gives \(X = +4\).
- In HCOOH:
- The equation is \(X + 1 + 2(-2) = 0\).
- Solving gives \(X = +2\).
- In HCHO:
- The equation is \(X + 1 + (-2) = 0\).
- Solving gives \(X = 0\).

3. **Conclusion on Assertion**: The oxidation state of Carbon varies in different compounds (e.g., +4 in CO₂, +2 in HCOOH, and 0 in HCHO). Therefore, the assertion is **false**.

### Step 2: Analyze the Reason
The reason states that "an element has a fixed oxidation state."

1. **Understanding Oxidation States**:
- Oxidation states can vary for elements depending on the compounds they are in. For example, Carbon can have oxidation states of +4, +2, or 0.
- Some elements, like Fluorine, do have a fixed oxidation state of -1 in all its compounds, but this is not true for all elements.

2. **Conclusion on Reason**: Since the oxidation state of Carbon is not fixed and can vary, the reason is also **false**.

### Final Conclusion
Both the assertion and the reason are false. Therefore, the correct answer is **Option D**: Both assertion and reason are false.

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