Identify the correct statement.

Options

A. Plaster of Paris can be obtained by hydeation of gypsum
B. Plaster of Paris is obtained by partial oxidation of gypsum
C. Gypsum contains a lower percentage of calcium than Plaster of Paris
D. Gypsum is obtained by heating Plaster of Paris

Answer

To solve the question of identifying the correct statement regarding plaster of Paris and gypsum, we will analyze each option step by step.

### Step 1: Understand the Compounds
- **Gypsum** is chemically represented as \( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \).
- **Plaster of Paris (POP)** is represented as \( \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} \) or \( \text{CaSO}_4 \cdot 0.5\text{H}_2\text{O} \).

### Step 2: Analyze Each Statement
1. **Option 1**: "Plaster of Paris can be obtained by the hydration of gypsum."
- **Analysis**: This statement is incorrect. Plaster of Paris is obtained by the dehydration of gypsum when it is heated, not by hydration.

2. **Option 2**: "Plaster of Paris is obtained by partial oxidation of gypsum."
- **Analysis**: This statement is also incorrect. Plaster of Paris is not formed through oxidation; it is formed through dehydration.

3. **Option 3**: "Gypsum contains a lower percentage of calcium than plaster of Paris."
- **Analysis**:
- In gypsum \( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \), there is 1 mole of calcium.
- In plaster of Paris \( \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} \), there is also 1 mole of calcium.
- However, the percentage of calcium in plaster of Paris is higher because it has less water content compared to gypsum.
- Thus, this statement is correct.

4. **Option 4**: "Gypsum is obtained by heating plaster of Paris."
- **Analysis**: This statement is incorrect. Gypsum cannot be obtained by heating plaster of Paris; rather, plaster of Paris is obtained by heating gypsum.

### Conclusion
After analyzing all the options, the correct statement is:
- **Option 3**: "Gypsum contains a lower percentage of calcium than plaster of Paris."