Which of the following are amphoteric ?

Options

A. `BeO`
B. `Al_2 O_3`
C. `ZnO`
D. `SO_2`

Answer

To determine which of the given substances are amphoteric, we need to analyze their ability to react with both acids and bases. Amphoteric substances can act as either an acid or a base depending on the reaction conditions.

### Step-by-Step Solution:

1. **Definition of Amphoteric Substances**:
- Amphoteric substances are those that can react with both acids and bases. This means they can donate protons (act as acids) or accept protons (act as bases).

2. **Analyzing Beryllium Oxide (BeO)**:
- Beryllium oxide reacts with sulfuric acid (an acid) to form beryllium sulfate and water:
\[ \text{BeO} + \text{H}_2\text{SO}_4 \rightarrow \text{BeSO}_4 + \text{H}_2\text{O} \]
- It also reacts with sodium hydroxide (a base) to form sodium beryllate and water:
\[ \text{BeO} + \text{NaOH} + \text{H}_2\text{O} \rightarrow \text{Na}_2\text{Be(OH)}_4 \]
- Since BeO reacts with both an acid and a base, it is amphoteric.

3. **Analyzing Aluminum Oxide (Al2O3)**:
- Aluminum oxide reacts with hydrochloric acid (an acid) to form aluminum ions and water:
\[ \text{Al}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\text{O} \]
- It also reacts with sodium hydroxide (a base) to form sodium aluminate:
\[ \text{Al}_2\text{O}_3 + 2\text{NaOH} + 3\text{H}_2\text{O} \rightarrow 2\text{NaAl(OH)}_4 \]
- Since Al2O3 reacts with both an acid and a base, it is amphoteric.

4. **Analyzing Zinc Oxide (ZnO)**:
- Zinc oxide reacts with hydrochloric acid (an acid) to form zinc ions and water:
\[ \text{ZnO} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2\text{O} \]
- It also reacts with sodium hydroxide (a base) to form sodium zincate:
\[ \text{ZnO} + 2\text{NaOH} + 2\text{H}_2\text{O} \rightarrow \text{Na}_2\text{Zn(OH)}_4 \]
- Since ZnO reacts with both an acid and a base, it is amphoteric.

5. **Analyzing Sulfur Dioxide (SO2)**:
- Sulfur dioxide is primarily an acidic oxide. It reacts with water to form sulfurous acid:
\[ \text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_3 \]
- It does not exhibit amphoteric behavior as it does not react with bases in the same manner as the other oxides. Therefore, SO2 is not amphoteric.

### Conclusion:
The amphoteric substances from the options provided are:
- Beryllium oxide (BeO)
- Aluminum oxide (Al2O3)
- Zinc oxide (ZnO)

### Final Answer:
**Beryllium oxide, Aluminum oxide, and Zinc oxide are amphoteric substances.**