A compound is prepared from gypsum upon heating to a temperature of `373` K. Which of the following is incorrect about this compound ?

Options

A. The formula of the compound is calcium sulphate dihydrate.
B. When mixed with water and left for half an hour, this compound sets into a hard mass.
C. If heated at higher temperature, the compound becomes dehydrated and is called dead burnt plaster.
D. Both (A) and (B)

Explanation

To solve the question, we need to analyze the information provided about the compound formed from gypsum when heated to a temperature of 373 K.

### Step-by-Step Solution:

1. **Identify Gypsum**:
- Gypsum is a mineral composed of calcium sulfate dihydrate, which has the chemical formula \( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \).

**Hint**: Remember that gypsum contains water molecules in its structure, which are important for its properties.

2. **Heating Gypsum**:
- When gypsum is heated to a temperature of 373 K (approximately 100°C), it undergoes a dehydration reaction where it loses its water of crystallization. This process converts gypsum into calcium sulfate hemihydrate.

**Hint**: Heating gypsum leads to the loss of water, transforming it into a different compound.

3. **Identify the New Compound**:
- The compound formed after heating gypsum is calcium sulfate hemihydrate, with the formula \( \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} \). This compound is commonly known as Plaster of Paris (POP).

**Hint**: The term "hemihydrate" indicates that the compound contains half a water molecule per formula unit.

4. **Evaluate Statements**:
- The question asks which statement about this compound is incorrect. We need to analyze the options provided (not explicitly listed in the question) and identify the one that does not accurately describe calcium sulfate hemihydrate.

5. **Conclusion**:
- Based on the information, if one of the statements claims that the compound retains its dihydrate form or has a different formula than \( \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} \), that statement would be incorrect.

**Hint**: Look for statements that misrepresent the chemical formula or properties of the compound formed from gypsum.

### Final Answer:
The incorrect statement about the compound formed from gypsum upon heating to 373 K is that it retains its dihydrate form; the correct form is calcium sulfate hemihydrate.