The formula of khadia (chalk) is

Options

A. `CaCO_(3)`
B. `MgCO_(3)`
C. CaO
D. `CaOCl_(2)`

Explanation

**Step-by-Step Solution:**

1. **Identify the Compound:** The question asks for the formula of khadia, which is commonly known as chalk.

2. **Determine the Chemical Formula:** Chalk is primarily composed of calcium carbonate. The chemical formula for calcium carbonate is \( \text{CaCO}_3 \).

3. **Understand the Composition:** Calcium carbonate consists of calcium ions (\( \text{Ca}^{2+} \)), carbonate ions (\( \text{CO}_3^{2-} \)). This combination forms the solid structure of chalk.

4. **Preparation of Chalk:** Chalk can be prepared by reacting calcium hydroxide with carbon dioxide. The reaction is as follows:
\[ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \]
Here, calcium hydroxide reacts with carbon dioxide to produce calcium carbonate (chalk) and water.

5. **Conclusion:** Therefore, the formula of khadia (chalk) is \( \text{CaCO}_3 \).

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