Assertion : Diabetes insipidus is marked by excessive urination and too much thirst for water.
Reason : Anti- diuretic hormone (ADH) is released by the posterior lobe of pituitary gland.

Options

A. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
B. If both Assertion and Reason are true, but the Reason is not the correct explanation of the 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 "Diabetes insipidus is marked by excessive urination and too much thirst for water."
- This condition is characterized by two main symptoms: polydipsia (excessive thirst) and polyuria (excessive urination).
- Therefore, the assertion is **true**.

2. **Understanding the Reason**:
- The reason states that "Anti-diuretic hormone (ADH) is released by the posterior lobe of the pituitary gland."
- ADH, also known as vasopressin, is indeed produced in the hypothalamus and stored in the posterior pituitary gland before being released into the bloodstream.
- The statement about ADH being released from the posterior pituitary gland is also **true**.

3. **Linking the Assertion and Reason**:
- The assertion describes the symptoms of diabetes insipidus, while the reason explains the role of ADH in regulating water balance in the body.
- Diabetes insipidus occurs due to a deficiency of ADH, which leads to the inability to concentrate urine, resulting in excessive urination and thirst.
- However, while the reason is true, it does not directly explain why diabetes insipidus causes excessive urination and thirst. It merely states where ADH is released from.

4. **Conclusion**:
- Both the assertion and the reason are true, but the reason does not correctly explain the assertion.
- Therefore, the final answer is: **Both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.**