Which of the following is a non-metal that remains liquid at room temperature?

Options

A. Bromine
B. Chlorine
C. Helium
D. Phosphorus

Explanation

To solve the question "Which of the following is a non-metal that remains liquid at room temperature?", we will analyze the given options step by step.

### Step-by-Step Solution:

1. **Identify the Non-Metals**:
We need to determine which of the given options are non-metals. Non-metals are elements that typically gain electrons during chemical reactions and have properties distinct from metals.

2. **Evaluate Each Option**:
- **Option 1: Bromine (Br)**
- Bromine is a non-metal with an atomic number of 35.
- At room temperature, bromine is in a liquid state.
- Therefore, this option is valid.

- **Option 2: Chlorine (Cl)**
- Chlorine is also a non-metal with an atomic number of 17.
- However, chlorine exists as a gas at room temperature.
- Thus, this option is incorrect.

- **Option 3: Helium (He)**
- Helium is a noble gas with an atomic number of 2.
- Noble gases are not considered non-metals in the traditional sense because they do not readily gain or lose electrons.
- Helium is also a gas at room temperature, making this option incorrect.

- **Option 4: Phosphorus (P)**
- Phosphorus is a non-metal with an atomic number of 15.
- At room temperature, phosphorus is solid.
- Therefore, this option is also incorrect.

3. **Conclusion**:
After evaluating all the options, the only non-metal that remains liquid at room temperature is **Bromine**.

### Final Answer:
The correct answer is **Bromine (Br)**.