Assertion : Henry's law is not obeyed by ammonia.
Reason : It reacts with water to form ammonium hydroxide.

Options

A. If both Assertion and Reason are CORRECT and a Reason is the CORRECT explanations of the Assertion
B. If both Assertion and Reason are CORRECT but Reason is not CORRECT explanation of the Assertion.
C. If Assertion is CORRECT but Reason is INCORRECT.
D. If Assertion is INCORRECT but Reason is CORRECT.

Answer

To solve the question regarding the assertion and reason related to Henry's law and ammonia, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Henry's Law**:
- Henry's law states that at a constant temperature, the amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of that gas above the liquid. This means that if you increase the pressure of the gas, more of it will dissolve in the liquid.

**Hint**: Remember that Henry's law applies when there is no chemical reaction between the gas and the solvent.

2. **Analyzing the Assertion**:
- The assertion states that "Henry's law is not obeyed by ammonia." To evaluate this, we need to consider the behavior of ammonia when it is dissolved in water.

**Hint**: Think about what happens to ammonia when it is mixed with water.

3. **Analyzing the Reason**:
- The reason given is that "it reacts with water to form ammonium hydroxide." This is a chemical reaction where ammonia (NH₃) reacts with water (H₂O) to produce ammonium hydroxide (NH₄OH).

**Hint**: Identify whether the reaction affects the solubility of ammonia in water.

4. **Connecting Assertion and Reason**:
- Since ammonia reacts with water to form ammonium hydroxide, it indicates that there is a chemical interaction. This means that the conditions of Henry's law are not met because the law assumes no chemical reaction occurs.

**Hint**: Recall that Henry's law is only valid for gases that do not chemically react with the solvent.

5. **Conclusion**:
- Both the assertion and the reason are correct. The assertion is true because ammonia does not obey Henry's law due to its reaction with water, which is explained by the reason provided.

**Final Answer**: Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.