Which of the following sublimes on heating ?

Options

A. `Al_(2)O_(3)`
B. `Al(OH)_(3)`
C. `(AlH_(3))_(pi)`
D. `(AlCl_(3))_(pi)`

Answer

To determine which of the given compounds sublimes upon heating, we need to analyze each option based on their physical states and properties. Here’s a step-by-step solution:

### Step 1: Understand Sublimation
Sublimation is the process where a solid turns directly into a gas upon heating without passing through the liquid state.

### Step 2: Analyze Each Option
1. **Alumina (Al₂O₃)**:
- This compound is a solid and has a very high melting point of about 2000°C.
- Since it does not easily convert to a liquid, it cannot sublime.
- **Conclusion**: Not the answer.

2. **Aluminum Hydroxide (Al(OH)₃)**:
- This is also a solid with a melting point around 300°C.
- Similar to alumina, it does not sublime as it requires high temperatures to decompose rather than sublime.
- **Conclusion**: Not the answer.

3. **Aluminum Hydride (AlH₃)**:
- AlH₃ exists as a dimer in liquid form.
- It does not sublime because it is not in a solid state at room temperature and does not transition directly to gas upon heating.
- **Conclusion**: Not the answer.

4. **Aluminum Chloride (AlCl₃)**:
- AlCl₃ can exist as a solid and, upon heating, it can sublime at around 180°C.
- When heated, it breaks down into gaseous forms, indicating that it undergoes sublimation.
- **Conclusion**: This is the correct answer.

### Final Answer
The compound that sublimes upon heating is **Aluminum Chloride (AlCl₃)**.