Hydrogen economy is use of Hydrogen as _________.

Answer

**Step-by-Step Solution:**

1. **Understanding the Term "Hydrogen Economy":**
- The term "Hydrogen economy" refers to a future scenario where hydrogen is used extensively as an energy carrier and fuel.

2. **Identifying the Role of Hydrogen:**
- In a hydrogen economy, hydrogen is primarily utilized as a fuel source. This means it can be used to power vehicles, generate electricity, and provide energy for various applications.

3. **Conclusion:**
- Therefore, the correct completion of the statement "Hydrogen economy is use of Hydrogen as _________" is "fuel".

**Final Answer:**
Hydrogen economy is use of Hydrogen as **fuel**.

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