When electricity is passed through water, then a change V occurs which leads to the formation of two gases W and X. On the other hand, when water is heated strongly, then a change Y takes place leading to the formation of gas Z.
What is the gas Z?

Answer

To solve the question, we need to analyze the two changes mentioned: the electrolysis of water and the heating of water.

### Step-by-Step Solution:

1. **Understanding Electrolysis of Water**:
- When electricity is passed through water (H₂O), it undergoes a process called electrolysis.
- During electrolysis, water is split into two gases: hydrogen (H₂) and oxygen (O₂).
- Therefore, we can identify the two gases formed as:
- Gas W = Hydrogen (H₂)
- Gas X = Oxygen (O₂)

2. **Identifying Change V**:
- The change that occurs when electricity is passed through water is called **Change V**.
- Change V = Electrolysis of Water.

3. **Heating Water**:
- When water is heated strongly, it undergoes a physical change where it transforms from a liquid state to a gaseous state.
- This process is known as vaporization.

4. **Identifying Gas Z**:
- The gas formed when water is heated strongly is water vapor, which is the gaseous form of water.
- Therefore, we can conclude that:
- Gas Z = Water vapor (H₂O in gaseous state).

5. **Identifying Change Y**:
- The change that occurs when water is heated strongly is called **Change Y**.
- Change Y = Vaporization of Water.

### Conclusion:
- The gas Z formed when water is heated strongly is **water vapor (H₂O)**.