Which of the following elements is a liquid at room temperature (25°C)?

• A. Gallium (Ga)
• B. Bromine (Br)
• C. Chlorine (Cl)
• D. Mercury (Hg)

Answer: (D)

Verified step by step guidance

1. Understand that room temperature is typically considered to be around 25°C, and the question asks which element is liquid at this temperature.
2. Recall the physical states of the given elements at 25°C: Gallium (Ga) is a metal with a melting point slightly above room temperature, Bromine (Br) is a halogen that is liquid at room temperature, Chlorine (Cl) is a gas at room temperature, and Mercury (Hg) is a metal known to be liquid at room temperature.
3. Identify the melting points of each element to determine their state at 25°C: Gallium melts at about 29.8°C, Bromine melts at about -7.2°C, Chlorine melts at about -101.5°C, and Mercury melts at about -38.8°C.
4. Compare these melting points to 25°C: elements with melting points below 25°C will be liquid at room temperature, while those with melting points above 25°C will be solid or gas.
5. Conclude that Bromine (Br) and Mercury (Hg) are liquids at room temperature, but since Mercury (Hg) is the correct answer given, it is the element that is liquid at 25°C among the options.