Which one of the following is used for drying of ammonia ?

Options

A. `conc. H_2 SO_4`
B. `CaO`
C. `P_2 O_5`
D. Anhydrous `CaCl_2`

Explanation

To determine which substance is used for drying ammonia, we can analyze the options provided:

1. **Concentrated Sulfuric Acid (H₂SO₄)**: This reacts with ammonia (NH₃) to form ammonium sulfate ((NH₄)₂SO₄). Therefore, it cannot be used for drying ammonia as it reacts with it.

2. **Calcium Oxide (CaO)**: This is a drying agent. It does not react with ammonia but instead absorbs moisture, making it suitable for drying gases, including ammonia.

3. **Phosphorus Pentoxide (P₂O₅)**: This also reacts with ammonia to form ammonium phosphate (NH₄)₃PO₄. Hence, it cannot be used for drying ammonia.

4. **Anhydrous Calcium Chloride (CaCl₂)**: This reacts with ammonia to form a complex (CaCl₂·8NH₃). Thus, it is not suitable for drying ammonia.

From the analysis, we can conclude that the only substance that does not react with ammonia and can effectively dry it is **Calcium Oxide (CaO)**.

### Final Answer:
**Calcium Oxide (CaO)** is used for drying ammonia.

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