Identify the correct statement regarding entropy

Options

A. At absolute zero of temperature, the entropy of all crystalline substances is taken to be zero
B. At absolute zero of temperature, the entropy of a perfectly crystalline substance is `+ve`
C. At absolute zero of temperature, entropy of a perfectly crystalline substance is taken to be zero
D. At `0^(@)C`, the entropy of a perfectly crystalline substance is taken to be zero.

Answer

To solve the question regarding the correct statement about entropy, we will analyze each statement provided in the question and apply the principles of thermodynamics, particularly the third law of thermodynamics.

### Step-by-Step Solution:

1. **Understanding the Statements**:
- **Statement 1**: "At absolute zero temperature, entropy of a crystalline substance is taken to be zero."
- **Statement 2**: "At absolute zero of temperature, entropy of a crystalline substance is positive."
- **Statement 3**: "At absolute zero of temperature, entropy of a pure crystalline substance is taken to be zero."

2. **Applying the Third Law of Thermodynamics**:
- The third law of thermodynamics states that as the temperature approaches absolute zero (0 Kelvin), the entropy of a perfect crystalline substance approaches zero. This means that at absolute zero, the entropy is exactly zero for a perfect crystal.

3. **Analyzing Each Statement**:
- **Statement 1**: This statement is correct because it aligns with the third law of thermodynamics.
- **Statement 2**: This statement is incorrect because it contradicts the third law; at absolute zero, the entropy cannot be positive.
- **Statement 3**: This statement is also correct as it reiterates that at absolute zero, the entropy of a pure crystalline substance is taken to be zero.

4. **Conclusion**:
- The correct statements regarding entropy are Statement 1 and Statement 3. Both indicate that at absolute zero temperature, the entropy of a crystalline substance is zero.

### Final Answer:
The correct statements regarding entropy are:
- Statement 1: "At absolute zero temperature, entropy of a crystalline substance is taken to be zero."
- Statement 3: "At absolute zero of temperature, entropy of a pure crystalline substance is taken to be zero."