Which oxide cannot be reduced by `H_2`?

Options

A. `Al_(2)O_(3)`
B. `CuO`
C. `ZnO`
D. All of these

Answer

To determine which oxide cannot be reduced by hydrogen, we need to consider the reactivity of the metals involved in the oxides. Here’s a step-by-step solution:

### Step 1: Understand Reduction
Reduction is a chemical reaction that involves the gain of electrons or a decrease in oxidation state. In the context of metal oxides, reduction typically involves converting the metal oxide back to its elemental form using a reducing agent, such as hydrogen.

### Step 2: Identify the Reactivity of Metals
The ability of hydrogen to reduce a metal oxide depends on the reactivity of the metal in the oxide. Metals that are more reactive than hydrogen cannot be reduced by hydrogen.

### Step 3: Refer to the Reactivity Series
The reactivity series of metals ranks metals from most reactive to least reactive. In this series:
- **Aluminium (Al)** and **Zinc (Zn)** are more reactive than hydrogen.
- **Copper (Cu)** is less reactive than hydrogen.

### Step 4: Analyze the Oxides
- For **Aluminium oxide (Al₂O₃)** and **Zinc oxide (ZnO)**: Since both aluminium and zinc are more reactive than hydrogen, they cannot be reduced by hydrogen.
- For **Copper oxide (CuO)**: Since copper is less reactive than hydrogen, it can be reduced by hydrogen.

### Step 5: Conclusion
The oxides that cannot be reduced by hydrogen are those of aluminium and zinc. Therefore, the correct answer is:
- Aluminium oxide (Al₂O₃)
- Zinc oxide (ZnO)

### Final Answer
The oxides that cannot be reduced by hydrogen are Aluminium oxide and Zinc oxide.

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