A. Lead
B. Silver
C. Mercury
D. Aluminium
Mercury is the only metal that remains in a liquid state at normal room temperature. Because of its unique properties, it was once widely used in thermometers, barometers, and scientific instruments.
Today, the use of mercury has declined because it is highly toxic and can damage the nervous system if people are exposed to it for long periods. Many countries now prefer safer alternatives in medical and laboratory equipment.