Assertion (A): Immune system becomes weak in old people.
Reason (R): Haemoglobin is less in the blood of old people.

Options

A. Both A and R are true and R is the correct explanation for A.
B. Both A and R are true, but R is not the correct explanation for A.
C. A is true and R is false.
D. A is false and R is true.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Assertion (A)**: The assertion states that the immune system becomes weak in old people. This is a well-established fact in biology. As people age, their immune response diminishes, making them more susceptible to infections and diseases.

2. **Understanding the Reason (R)**: The reason provided is that hemoglobin levels are lower in the blood of old people. Hemoglobin is crucial for transporting oxygen in the blood, and lower levels can contribute to fatigue and weakness.

3. **Analyzing the Connection**: While it is true that older adults may have lower hemoglobin levels, this does not directly explain why their immune system weakens. The weakening of the immune system is primarily due to changes in the bone marrow and thymus gland function, which affects the production of white blood cells (WBCs) that are essential for immune response.

4. **Conclusion**: Both the assertion and the reason are true statements, but the reason does not adequately explain the assertion. Therefore, the assertion is correct, but the reason is not the correct explanation for the assertion.

5. **Final Answer**: The correct option is that both the assertion and reason are true, but the reason is not the correct explanation for the assertion.

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