Which of the following changes directly from solid to gas on heating?

Options

A. Ammonium chloride
B. Sodium chloride
C. Potassium chloride
D. Calcium chloride

Explanation

To determine which of the following compounds changes directly from solid to gas upon heating, we need to identify the process known as sublimation. Sublimation occurs when a solid transitions directly into a gas without passing through the liquid state.

### Step-by-Step Solution:

1. **Understand the Concept of Sublimation**:
- Sublimation is the process where a solid turns directly into a gas when heated, bypassing the liquid phase.

2. **Analyze the Options**:
- We have four compounds to consider:
- Option 1: Ammonium Chloride (NH4Cl)
- Option 2: Sodium Chloride (NaCl)
- Option 3: Potassium Chloride (KCl)
- Option 4: Calcium Chloride (CaCl2)

3. **Evaluate Each Compound**:
- **Option 1: Ammonium Chloride (NH4Cl)**:
- When heated, NH4Cl dissociates into ammonia gas (NH3) and hydrogen chloride gas (HCl). This indicates that it sublimates, transitioning directly from solid to gas.
- **Option 2: Sodium Chloride (NaCl)**:
- When heated, NaCl does not dissociate into gases; it remains solid until it melts into a liquid.
- **Option 3: Potassium Chloride (KCl)**:
- Similar to NaCl, KCl does not sublime; it remains solid or melts into a liquid upon heating.
- **Option 4: Calcium Chloride (CaCl2)**:
- CaCl2 also does not sublime; it remains solid or melts when heated.

4. **Conclusion**:
- The only compound that sublimates, changing directly from solid to gas, is **Ammonium Chloride (NH4Cl)**. Therefore, the correct answer is **Option 1**.

### Final Answer:
**Ammonium Chloride (NH4Cl)** is the compound that changes directly from solid to gas on heating.