Which one of the following is liquid at room temperature?

Options

A. `CH_3Cl`
B. `C_2H_5Cl`
C. `CH_3Br`
D. `C_2H_5Br`

Answer

To determine which of the following compounds is liquid at room temperature, we will analyze each option based on their molecular structure and boiling points.

### Step-by-Step Solution:

1. **Identify the Compounds**:
Let's consider the compounds given in the options:
- Option 1: CH3Cl (Chloromethane)
- Option 2: C2H5Cl (Chloroethane)
- Option 3: C2H5Br (Bromoethane)
- Option 4: CH3Br (Bromomethane)

2. **Check the Physical State at Room Temperature**:
- **CH3Cl (Chloromethane)**: It has a boiling point of approximately -23.8 °C, which means it is a gas at room temperature.
- **C2H5Cl (Chloroethane)**: This compound is also a gas at room temperature.
- **C2H5Br (Bromoethane)**: This compound has a boiling point around 38 °C, indicating that it is a liquid at room temperature.
- **CH3Br (Bromomethane)**: It has a boiling point of about 3.2 °C, which means it is also a liquid at room temperature.

3. **Conclusion**:
Based on the boiling points, we find that both C2H5Br and CH3Br are liquids at room temperature. However, if we are to choose one, C2H5Br (Bromoethane) is the more common answer as it is a larger molecule with a higher molecular mass, which contributes to its liquid state at room temperature.

### Final Answer:
**C2H5Br (Bromoethane) is liquid at room temperature.**