The correct option is **C. Bromine**. ### Detailed Explanation: 1. **Understanding Non-Metals**: Non-metals are elements that typically lack the characteristics of metals. They are usually poor conductors of heat and electricity, have lower densities, and can exist in various states (solid, liquid, gas) at room temperature. 2. **Identifying the Elements**: - **Chlorine (Cl)**: Chlorine is a non-metal that exists as a gas at room temperature. It has a boiling point of -34.04 °C, which means it is gaseous under standard conditions. - **Phosphorus (P)**: Phosphorus is a non-metal that primarily exists as a solid at room temperature. It has several allotropes, with white phosphorus being the most common, which has a melting point of about 44.1 °C. - **Bromine (Br)**: Bromine is unique among the non-metals listed here because it is the only one that is a liquid at room temperature. It has a boiling point of 58.8 °C and a melting point of -7.2 °C, allowing it to remain in liquid form under standard conditions. - **Helium (He)**: Helium is a noble gas and is also a non-metal. However, it is a gas at room temperature, with a boiling point of -268.93 °C. 3. **Why Bromine is Correct**: - Bromine is the only non-metal that is liquid at room temperature. Its physical state is due to its molecular structure and intermolecular forces. Bromine molecules (Br2) are held together by relatively weak van der Waals forces, which allows them to remain in a liquid state at temperatures that are higher than those of other non-metals. 4. **Why Other Options are Incorrect**: - **Chlorine (A)**: Incorrect because it is a gas at room temperature. - **Phosphorus (B)**: Incorrect because it is a solid at room temperature. - **Helium (D)**: Incorrect because it is a gas at room temperature. ### Summary of Key Points: - **Bromine (Br)** is the only non-metal that is liquid at room temperature. - **Chlorine** and **Helium** are gases, while **Phosphorus** is a solid at room temperature. - Understanding the states of matter and the properties of elements is crucial for identifying their physical forms under standard conditions. ### Revision Summary: - Bromine is the only liquid non-metal at room temperature. - Chlorine and Helium are gases; Phosphorus is a solid. - Familiarize yourself with the states of elements and their boiling/melting points for better understanding.