Assertion : White phosphorus is more reactive than red phosphorus.
Reason : It readily catches fire in air to give dense white fumes of `P_(4)O_(10)`.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

To solve the question regarding the assertion and reason about the reactivity of white phosphorus compared to red phosphorus, we can break it down into clear steps:

### Step 1: Understand the Assertion
The assertion states that "White phosphorus is more reactive than red phosphorus."

- **Explanation**: White phosphorus (P4) has a tetrahedral structure with four phosphorus atoms that are closely packed. This structure has less steric hindrance compared to red phosphorus, which has a polymeric structure with chains of phosphorus atoms. The lack of steric hindrance in white phosphorus allows it to react more readily with other substances, making it more reactive.

### Step 2: Understand the Reason
The reason provided is that "It readily catches fire in air to give dense white fumes of P4O10."

- **Explanation**: When white phosphorus is exposed to air, it reacts with oxygen and combusts, producing phosphorus pentoxide (P4O10), which appears as dense white fumes. This reaction is a characteristic of its high reactivity. However, this statement alone does not explain why white phosphorus is more reactive than red phosphorus.

### Step 3: Analyze the Relationship
Now, we need to analyze the relationship between the assertion and the reason.

- **Assertion**: White phosphorus is indeed more reactive than red phosphorus.
- **Reason**: While it is true that white phosphorus catches fire and produces P4O10, this fact does not explain why it is more reactive than red phosphorus. The reason is more about the physical structure and steric factors rather than just the combustion reaction.

### Step 4: Conclusion
Based on the analysis:
- Both the assertion and the reason are true.
- However, the reason does not correctly explain the assertion.

Thus, the correct conclusion is that both the assertion and reason are true, but the reason is not the correct explanation for the assertion.

### Final Answer
Both the assertion and reason are true, but the reason is not the correct explanation for the assertion.

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