Which of the following elements is liquid at room temperature?

The correct answer is Bromine. Bromine (Br) is one of only two elements that are liquid at standard room temperature and pressure (approximately 20-25°C), the other being mercury. It is a reddish-brown, volatile liquid.

• Silicon is a metalloid that is solid at room temperature.
• Gallium is a metal that melts at 29.76°C, which is slightly above typical room temperature, though it can melt in a warm hand. However, Bromine is definitively liquid at standard room temperature.
• Option D is empty and not a valid element.