Identify the correct statement.

Options

A. (a) Gypsum is obtained by heating plaster of Paris
B. (b) Plastic of Paris can be obtained by hydration of gypsum
C. (c) Plaster of Paris is obtained by partial oxidation of gypsum
D. (d) Gypsum contains a lower percentage of calcium than plaster of Paris

Explanation

To identify the correct statement regarding gypsum and plaster of Paris, let's analyze each option step by step.

### Step 1: Understand the Chemical Composition
- **Gypsum** is chemically represented as **CaSO4·2H2O** (calcium sulfate dihydrate).
- **Plaster of Paris (POP)** is represented as **CaSO4·0.5H2O** (calcium sulfate hemihydrate).

### Step 2: Analyze Each Statement
1. **Option A**: Gypsum is obtained by heating plaster of Paris.
- This statement is incorrect. Gypsum cannot be obtained by heating plaster of Paris; rather, plaster of Paris is obtained by heating gypsum.

2. **Option B**: Plaster of Paris can be obtained by hydration of gypsum.
- This statement is also incorrect. Plaster of Paris is obtained by heating gypsum, not by hydration.

3. **Option C**: Plaster of Paris is obtained by partial oxidation of gypsum.
- This statement is incorrect. Plaster of Paris is not obtained through oxidation; it is specifically obtained by heating gypsum.

4. **Option D**: Gypsum contains a lower percentage of calcium than plaster of Paris.
- To analyze this, we can calculate the percentage of calcium in both compounds:
- For gypsum (CaSO4·2H2O):
- Molar mass of Ca = 40.08 g/mol
- Molar mass of CaSO4·2H2O = 40.08 + 32.07 + (4 × 16.00) + (2 × 18.02) = 172.17 g/mol
- Percentage of calcium = (40.08 / 172.17) × 100 ≈ 23.26%
- For plaster of Paris (CaSO4·0.5H2O):
- Molar mass of CaSO4·0.5H2O = 40.08 + 32.07 + (4 × 16.00) + (0.5 × 18.02) = 146.15 g/mol
- Percentage of calcium = (40.08 / 146.15) × 100 ≈ 27.43%
- Since plaster of Paris has a higher percentage of calcium than gypsum, this statement is correct.

### Conclusion
- The correct statement is **Option D**: Gypsum contains a lower percentage of calcium than plaster of Paris.