A: Solubility of gas increases on increasing pressure.
R: Solubility of gas decreases on decreasing the temperature.

Answer

To solve the assertion-reason question, we will analyze both the assertion (A) and the reason (R) step by step.

### Step 1: Analyze the Assertion (A)
**Assertion:** Solubility of gas increases on increasing pressure.

- According to Henry's Law, the solubility of a gas in a liquid is directly proportional to the pressure of that gas above the liquid. This means that as the pressure increases, the solubility of the gas in the liquid also increases. Therefore, the assertion is **correct**.

### Step 2: Analyze the Reason (R)
**Reason:** Solubility of gas decreases on decreasing the temperature.

- The solubility of gases in liquids is generally inversely related to temperature. As temperature decreases, the kinetic energy of the gas molecules decreases, allowing more gas to dissolve in the liquid. Conversely, when the temperature increases, the solubility of the gas decreases. Thus, the reason is also **correct**.

### Step 3: Determine the Relationship Between A and R
- The reason provided explains the assertion. The increase in pressure (assertion) leads to an increase in solubility, while the decrease in temperature (reason) also supports the idea that solubility can be affected by external conditions. Therefore, the reason is a correct explanation of the assertion.

### Conclusion
Both the assertion and the reason are correct, and the reason is the correct explanation of the assertion.

### Final Answer
- **Assertion (A): Correct**
- **Reason (R): Correct**
- **Relationship:** R is the correct explanation of A.

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