The correct answer is A. Mercury.
Mercury is the only non-metal that turns into liquid at room temperature. It is a silvery-white liquid that is very dense and has a high surface tension. Mercury is also a very good conductor of electricity and heat. It is used in thermometers, barometers, and other scientific instruments.
Bromine is a red-brown liquid that is also a non-metal. It is a very reactive element and is used in a variety of industrial applications. Chlorine is a greenish-yellow gas that is also a non-metal. It is a very reactive element and is used in a variety of industrial applications. Gallium is a silvery-white metal that melts at a very low temperature of 29.76 degrees Celsius. It is used in a variety of electronic devices.
Mercury is the only non-metal that turns into liquid at room temperature because it has a very low melting point. The melting point of a substance is the temperature at which it changes from a solid to a liquid. The melting point of mercury is -38.83 degrees Celsius, which is much lower than the melting point of any other non-metal. This is because mercury has a very weak atomic bond. The atoms in mercury are not held together very strongly, so they can easily move around and change from a solid to a liquid.