Two volumes of hydrogen and one volume of oxygen compose one volume of water.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Components:**
- We start with the components involved in the reaction: hydrogen (H₂) and oxygen (O₂).
- According to the question, we have 2 volumes of hydrogen and 1 volume of oxygen.

2. **Chemical Reaction:**
- The chemical reaction for the formation of water (H₂O) can be written as:
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