State Gay-Lussac.s Law of combining volumes.

Explanation

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

1. **Definition of Gay-Lussac's Law of Combining Volumes:**
Gay-Lussac's Law of Combining Volumes states that when gases react together at constant temperature and pressure, the volumes of the reacting gases and the volumes of the products (if gaseous) are in simple whole number ratios.

2. **Explanation of the Law:**
This law implies that if we take two or more gaseous reactants, they will combine to form one or more gaseous products, and the volumes of these gases will be in a ratio of small whole numbers.

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