Identify the correct statement

Options

A. Gypsum contains a lower percentage of calcium than plaster of paris
B. Gypsum is obtained by heating plaster of paris
C. Plaster of paris can be obtained by hydration of gypsum
D. None of these

Answer

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

### Step 1: Understand the Chemical Formulas
- **Gypsum**: The chemical formula for gypsum is \( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \).
- **Plaster of Paris**: The chemical formula for plaster of Paris is \( \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} \) or \( \text{CaSO}_4 \cdot H_2O \) (often written as \( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \) when considering the dehydration process).

### Step 2: Analyze Option 1
- **Option 1**: "Gypsum contains a lower percentage of calcium than plaster of Paris."
- In gypsum, there is 1 calcium atom.
- In plaster of Paris, there are 2 calcium atoms.
- Therefore, gypsum does indeed have a lower percentage of calcium compared to plaster of Paris.
- **Conclusion**: This statement is **correct**.

### Step 3: Analyze Option 2
- **Option 2**: "Gypsum is obtained by heating plaster of Paris."
- This statement is incorrect because plaster of Paris is produced by heating gypsum, not the other way around.
- **Conclusion**: This statement is **incorrect**.

### Step 4: Analyze Option 3
- **Option 3**: "Plaster of Paris can be obtained by hydration."
- This statement is also incorrect because plaster of Paris is formed by the dehydration of gypsum, not hydration.
- **Conclusion**: This statement is **incorrect**.

### Step 5: Analyze Option 4
- **Option 4**: "None of these."
- Since we have already established that Option 1 is correct, this statement is also incorrect.
- **Conclusion**: This statement is **incorrect**.

### Final Conclusion
The correct statement among the options provided is **Option 1**: "Gypsum contains a lower percentage of calcium than plaster of Paris."

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