Assertion: Antidiuretic hormone (ADH) controls the amount of water in the urine.
Reason: ADH determines the permeability of the collecting duct to water.

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

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that Antidiuretic hormone (ADH) controls the amount of water in the urine. This is true because ADH plays a crucial role in regulating water balance in the body.

2. **Understanding the Reason**: The reason provided states that ADH determines the permeability of the collecting duct to water. This is also true. ADH increases the permeability of the collecting duct, allowing more water to be reabsorbed back into the bloodstream.

3. **Mechanism of Action**: ADH is produced in the hypothalamus and released from the posterior pituitary gland. When the body experiences water loss, osmoreceptors in the body detect this change and stimulate the release of ADH.

4. **Effect of ADH**: Once released, ADH acts on the distal convoluted tubule (DCT) and the collecting duct of the nephron. It increases the permeability of these structures to water, leading to greater reabsorption of water back into the bloodstream and thus reducing the volume of urine produced.

5. **Conclusion**: Both the assertion and the reason are true statements. The reason correctly explains the assertion, as the action of ADH in increasing the permeability of the collecting duct directly influences the amount of water that is reabsorbed, thereby controlling the volume of urine.

### Final Answer:
Both the assertion and reason are true, and the reason is the correct explanation for the assertion.

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