The metal oxide which is reduced by hydrogen is:

Options

A. `Al_2O_3`
B. CuO
C. CaO
D. `Na_2O`

Explanation

To determine which metal oxide can be reduced by hydrogen, we can follow these steps:

### Step 1: Understand the Reactivity Series
The reactivity series is a list of metals arranged in order of decreasing reactivity. The more reactive a metal is, the higher it appears in the series. Hydrogen is included in the series and is used as a reference point for the reactivity of metals.

### Step 2: Identify the Metal Oxides Given
The question provides several metal oxides. We need to analyze each one to see if the metal in the oxide is below hydrogen in the reactivity series.

### Step 3: Analyze Each Option
1. **Al₂O₃ (Aluminum Oxide)**:
- Aluminum (Al) is above hydrogen in the reactivity series. Therefore, hydrogen cannot reduce Al₂O₃.

2. **CuO (Copper Oxide)**:
- Copper (Cu) is below hydrogen in the reactivity series. Therefore, hydrogen can reduce CuO to copper.
- The reaction is: CuO + H₂ → Cu + H₂O (removal of oxygen indicates reduction).

3. **CaO (Calcium Oxide)**:
- Calcium (Ca) is above hydrogen in the reactivity series. Therefore, hydrogen cannot reduce CaO.

4. **Na₂O (Sodium Oxide)**:
- Sodium (Na) is also above hydrogen in the reactivity series. Therefore, hydrogen cannot reduce Na₂O.

### Step 4: Conclusion
Based on the analysis, the only metal oxide that can be reduced by hydrogen is **CuO (Copper Oxide)**.

### Final Answer
The metal oxide which is reduced by hydrogen is **CuO**.

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