Which of the following salts does not contain water of crystallization?

Options

A. Blue vitriol
B. Baking soda
C. washing soda
D. Gypsum

Explanation

To determine which of the following salts does not contain water of crystallization, we will analyze each option mentioned in the video transcript.

1. **Baking Soda (Sodium Hydrogen Carbonate)**:
- Chemical formula: NaHCO₃
- Water of crystallization: **None**. Baking soda does not contain any water of crystallization.

2. **Washing Soda (Sodium Carbonate Decahydrate)**:
- Chemical formula: Na₂CO₃·10H₂O
- Water of crystallization: **10**. This salt contains 10 molecules of water of crystallization.

3. **Gypsum (Calcium Sulfate Dihydrate)**:
- Chemical formula: CaSO₄·2H₂O
- Water of crystallization: **2**. Gypsum contains 2 molecules of water of crystallization.

4. **Calcium Sulfate (Plaster of Paris)**:
- Chemical formula: CaSO₄
- Water of crystallization: **None**. Plaster of Paris does not contain any water of crystallization.

From the analysis above, we can conclude that:

- **Baking Soda (NaHCO₃)** does not contain water of crystallization.
- **Plaster of Paris (CaSO₄)** also does not contain water of crystallization.

However, since the question asks for one salt, the most commonly recognized salt that does not contain water of crystallization is **Baking Soda (NaHCO₃)**.

### Final Answer:
Baking Soda (NaHCO₃) does not contain water of crystallization.