State Henry's law.

Explanation

**Step-by-Step Text Solution:**

1. **Definition of Henry's Law**: Henry's law states that at a constant temperature, the amount of gas that dissolves in a liquid is directly proportional to the partial pressure of that gas above the liquid.

2. **Explanation of the Law**: This means that if you increase the pressure of the gas above the liquid, more gas will dissolve in the liquid. Conversely, if the pressure decreases, the solubility of the gas in the liquid will also decrease.

3. **Mathematical Representation**: The relationship can be expressed mathematically as:
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