A compound is prepared from gypsum upon heating to a temperature of 373 K and it changes back to gypsum on adding water. Which is the incorrect statement about the compound?

Options

A. The compound is used for setting fractured bones.
B. The compound is called plaster of Paris which is calcium sulphate dehydrate with a formula `CaSO_(4).2HO`.
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 given about the compound prepared from gypsum and determine which statement is incorrect. Here’s a step-by-step solution:

### Step 1: Identify Gypsum and Its Formula
Gypsum is a mineral composed of calcium sulfate dihydrate. Its chemical formula is:
\[ \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \]

### Step 2: Heating Gypsum
When gypsum is heated to a temperature of 373 K (which is approximately 100 °C), it loses water and transforms into a different compound known as Plaster of Paris. The reaction can be represented as:
\[ \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \xrightarrow{\text{heat}} \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} + \text{1.5H}_2\text{O} \text{ (as steam)} \]

### Step 3: Identify the Compound Formed
The compound formed after heating gypsum is called Plaster of Paris, which has the formula:
\[ \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} \]
This is also referred to as calcium sulfate hemihydrate.

### Step 4: Rehydration of Plaster of Paris
When water is added to Plaster of Paris, it rehydrates and converts back to gypsum:
\[ \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} + \text{1.5H}_2\text{O} \rightarrow \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \]

### Step 5: Analyze the Statements
Now, we need to evaluate the statements provided in the question to find the incorrect one:

1. **The compound is used for setting fractured bones.**
- This statement is correct. Plaster of Paris is indeed used for this purpose.

2. **The compound is called Plaster of Paris which is Calcium Sulfate Dihydrate with the formula CaSO4.2H2O.**
- This statement is incorrect. Plaster of Paris is calcium sulfate hemihydrate, not dihydrate. Its correct formula is CaSO4.1/2H2O.

3. **If heated at higher temperature the compound becomes dehydrated and is called dead burnt plaster.**
- This statement is correct. Heating Plaster of Paris at higher temperatures leads to the formation of anhydrous calcium sulfate, known as dead burnt plaster.

4. **Both A and B.**
- This statement is also incorrect because statement A is correct.

### Conclusion
The incorrect statement about the compound is:
**The compound is called Plaster of Paris which is Calcium Sulfate Dihydrate with the formula CaSO4.2H2O.**