Plaster of paris is :

Options

A. `CaSO_(4)`
B. `CaSO_(4)*7H_(2)O`
C. `2CaSO_(4)*H_(2)O`
D. `CaSO_(4)*2H_(2)O`

Answer

To determine what plaster of Paris is, we need to analyze the options given and identify the correct chemical formula associated with plaster of Paris.

### Step-by-Step Solution:

1. **Understanding Plaster of Paris**:
- Plaster of Paris is a building material based on calcium sulfate. It is created by heating gypsum (calcium sulfate dihydrate) to remove water.

2. **Identifying the Chemical Formula**:
- The chemical formula for gypsum is \( CaSO_4 \cdot 2H_2O \) (calcium sulfate dihydrate).
- When gypsum is heated, it loses water and forms plaster of Paris, which has the formula \( CaSO_4 \cdot \frac{1}{2}H_2O \) or \( CaSO_4 \cdot 1.2H_2O \) (calcium sulfate hemihydrate).

3. **Analyzing the Options**:
- **Option A**: \( CaSO_4 \) - This is just calcium sulfate without any water.
- **Option B**: \( CaSO_4 \cdot 7H_2O \) - This is calcium sulfate heptahydrate, not plaster of Paris.
- **Option C**: \( 2CaSO_4 \cdot H_2O \) - This represents calcium sulfate hemihydrate, which is indeed plaster of Paris.
- **Option D**: \( CaSO_4 \cdot 2H_2O \) - This is gypsum, not plaster of Paris.

4. **Conclusion**:
- The correct answer is **Option C**: \( 2CaSO_4 \cdot H_2O \), which is the chemical formula for plaster of Paris.

### Final Answer:
Plaster of Paris is \( 2CaSO_4 \cdot H_2O \).

---