Assertion: Hormone calcitonin has antagonistic effect to that of parathormone.
Reason: Calcitonin decreases blood calcium level while parathormone increases blood calcium level.

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, we need to analyze both the assertion and the reason provided.

### Step-by-step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Hormone calcitonin has an antagonistic effect to that of parathormone."
- This means that calcitonin and parathormone have opposing effects on the body, particularly concerning calcium levels in the blood.

**Hint**: Look for the definitions and functions of calcitonin and parathormone to understand their roles in calcium regulation.

2. **Understanding the Reason**:
- The reason states that "Calcitonin decreases blood calcium level while parathormone increases blood calcium level."
- This is a factual statement about the functions of these hormones. Calcitonin, produced by the thyroid gland, helps lower blood calcium levels by promoting calcium deposition in bones and increasing calcium excretion in urine. In contrast, parathormone, produced by the parathyroid glands, raises blood calcium levels by stimulating calcium release from bones, increasing calcium absorption in the intestines, and reducing calcium excretion in urine.

**Hint**: Identify the specific actions of each hormone to see how they affect blood calcium levels.

3. **Evaluating the Relationship**:
- Since calcitonin decreases blood calcium levels and parathormone increases them, they indeed have antagonistic effects.
- Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

**Hint**: Consider how the actions of these hormones relate to one another to determine if they are truly antagonistic.

4. **Conclusion**:
- Both the assertion and reason are true, and the reason provides a correct explanation for the assertion. Thus, the correct answer is that both statements are true, and the reason is a valid explanation for the assertion.

**Hint**: Look for options that confirm both statements as true and that the reason explains the assertion.

### Final Answer:
Both the assertion and reason are true, and the reason correctly explains the assertion.