Gypsum `CaSO_(4).2H_(2)O` on heating about `120^(@)C` forms a compound which has the chemical composition is

Options

A. `CaSO_(4)`
B. `2CaSO_(4).H_(2)O`
C. `CaSO_(4).H_(2)O`
D. `2CaSO_(4).3H_(2)O`

Explanation

To solve the question regarding the heating of gypsum (CaSO₄·2H₂O) and the compound it forms, we can follow these steps:

### Step 1: Understand the Composition of Gypsum
Gypsum is chemically represented as CaSO₄·2H₂O. This means it consists of calcium sulfate (CaSO₄) and two water molecules (2H₂O) associated with it.

### Step 2: Heating Gypsum
When gypsum is heated to about 120°C, it undergoes a dehydration process. The heat causes the water molecules to evaporate.

### Step 3: Identify the Dehydration Process
During the dehydration of gypsum, one of the water molecules is removed. The reaction can be represented as:
\[ \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \rightarrow \text{CaSO}_4 \cdot \text{H}_2\text{O} + \text{H}_2\text{O} \]

### Step 4: Determine the Resulting Compound
After the removal of one water molecule, the compound formed is calcium sulfate hemihydrate, which is represented as CaSO₄·(1/2)H₂O or more commonly as CaSO₄·H₂O. This compound is also known as plaster of Paris (POP).

### Step 5: Write the Final Chemical Composition
The final compound formed after heating gypsum at 120°C is:
\[ \text{CaSO}_4 \cdot \text{H}_2\text{O} \]

### Conclusion
Thus, the compound formed from gypsum upon heating at 120°C is calcium sulfate hemihydrate, which can be represented as:
\[ \text{CaSO}_4 \cdot \text{H}_2\text{O} \]