Explanation: In the context of Indian General Knowledge (GK), understanding the physical states of elements at room temperature is crucial, especially for competitive examinations. Non-metals are a class of elements that do not conduct electricity and heat well, and they are typically found in the right side of the periodic table. Most non-metals are gases at room temperature, such as oxygen, nitrogen, and chlorine. However, there are exceptions to this general rule.
One such exception is bromine, which is a non-metal that remains liquid at room temperature. Bromine is a halogen, a group of elements known for their reactivity and their ability to form salts. The halogen group includes fluorine, chlorine, bromine, iodine, and astatine. Among these, bromine is the only one that is liquid at room temperature. This unique property makes bromine a significant element to remember in the context of non-metals and their physical states.
To understand why bromine is liquid at room temperature, we need to consider its atomic structure and intermolecular forces. Bromine has a relatively low melting point of -7.2°C (19.0°F) and a boiling point of 58.8°C (137.8°F). This means that at room temperature (approximately 20-25°C), bromine is in its liquid state. The intermolecular forces in bromine are weaker than those in iodine, which is a solid at room temperature, but stronger than those in chlorine, which is a gas. This balance of forces allows bromine to remain liquid under normal conditions.
In contrast, the other options provided are incorrect for the following reasons:
- Phosphorous (Option A) is a solid non-metal at room temperature.
- Chlorine (Option C) is a gas at room temperature.
- Helium (Option D) is also a gas at room temperature.
Therefore, bromine is the only non-metal that remains liquid at room temperature, making it the correct answer to this question. Understanding the unique properties of elements like bromine is essential for mastering the periodic table and the physical states of elements, which are important topics in Indian GK and competitive examinations.