Which of the following is most volatile ?

Options

A. `H_2O`
B. `H_2S`
C. `H_2Se`
D. `H_2Te`

Explanation

To determine which of the given hydrides (H2O, H2S, H2Se, H2Te) is the most volatile, we will analyze their molecular weights and the presence of hydrogen bonding.

### Step-by-Step Solution:

1. **Understanding Volatility**:
- Volatility refers to how easily a substance can be converted into a gas. Generally, lower molecular weight compounds tend to be more volatile.

2. **Molecular Weights Calculation**:
- Calculate the molecular weights of each hydride:
- **H2O**:
- H: 1 g/mol (2 H atoms) = 2 g/mol
- O: 16 g/mol
- Total = 2 + 16 = **18 g/mol**
- **H2S**:
- H: 1 g/mol (2 H atoms) = 2 g/mol
- S: 32 g/mol
- Total = 2 + 32 = **34 g/mol**
- **H2Se**:
- H: 1 g/mol (2 H atoms) = 2 g/mol
- Se: 79 g/mol
- Total = 2 + 79 = **81 g/mol**
- **H2Te**:
- H: 1 g/mol (2 H atoms) = 2 g/mol
- Te: 128 g/mol
- Total = 2 + 128 = **130 g/mol**

3. **Order of Molecular Weights**:
- Based on the calculations:
- H2O: 18 g/mol
- H2S: 34 g/mol
- H2Se: 81 g/mol
- H2Te: 130 g/mol
- The order of increasing molecular weight is: H2O < H2S < H2Se < H2Te.

4. **Considering Hydrogen Bonding**:
- H2O has extensive hydrogen bonding due to its highly polar O-H bonds. This strong intermolecular force significantly reduces its volatility.
- H2S does not exhibit hydrogen bonding to the same extent, making it more volatile than H2O.

5. **Final Conclusion**:
- Although H2O has the lowest molecular weight, its hydrogen bonding makes it less volatile than H2S.
- Therefore, the most volatile hydride among the given options is **H2S**.

### Answer:
The most volatile hydride is **H2S** (Option B).

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