Assertion :- Deficiency of vitamin -D causes rickets.
Reason:- It is obtained from intrinsic sources regularly

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.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Deficiency of vitamin D causes rickets."
- This is a true statement. Vitamin D is essential for calcium absorption in the body, and its deficiency leads to rickets, which is characterized by the softening and weakening of bones in children.

2. **Understanding the Reason**:
- The reason given is "It is obtained from intrinsic sources regularly."
- While vitamin D can be synthesized in the skin upon exposure to sunlight (an intrinsic source), it can also be obtained from dietary sources (extrinsic). Therefore, the statement is somewhat misleading as it implies that vitamin D is only obtained from intrinsic sources.

3. **Evaluating the Relationship**:
- The assertion is true, but the reason does not correctly explain why vitamin D deficiency leads to rickets. The reason provided does not directly relate to the cause of rickets.

4. **Analyzing the Options**:
- Option 1: Both assertion and reason are true, and reason is the correct explanation of assertion. (Incorrect)
- Option 2: Both assertion and reason are true, and reason is not the correct explanation of assertion. (Correct)
- Option 3: Assertion is true, and reason is false. (Incorrect)
- Option 4: Both assertion and reason are false. (Incorrect)

5. **Conclusion**:
- The correct answer is Option 2: Both assertion and reason are true, but the reason is not the correct explanation of the assertion.