Explanations:Understanding the physical states of elements at room temperature is a fundamental concept in chemistry. Elements can exist in solid, liquid, or gaseous states depending on their temperature and pressure conditions. The state of an element at room temperature is determined by its melting and boiling points.
Metals and non-metals are two broad categories of elements. Metals are typically solid at room temperature, with a few exceptions like mercury, which is a liquid metal. Non-metals, on the other hand, can be gases, liquids, or solids at room temperature. The majority of non-metals are gases, such as hydrogen, oxygen, nitrogen, and the halogens (fluorine and chlorine).
Bromine is a unique non-metal because it is the only one that is liquid at room temperature. Bromine is a halogen, and it has a melting point of -7.2°C and a boiling point of 58.8°C. This means that at room temperature (approximately 20-25°C), bromine exists as a liquid. Its liquid state at room temperature is due to its relatively low melting point compared to other non-metals.
Other non-metals like phosphorous, chlorine, and helium do not meet the criteria of being liquid at room temperature. Phosphorous is a solid non-metal with a melting point of 44.1°C, making it solid at room temperature. Chlorine is a gas with a boiling point of -34.04°C, and helium is also a gas with a boiling point of -268.93°C. Both chlorine and helium are gases at room temperature.
Therefore, the correct answer is bromine, as it is the only non-metal that is liquid at room temperature. This property makes bromine unique among non-metals and is an important characteristic to remember in chemistry.