The correct answer is lithium. Lithium is a soft, silvery-white metal that is the lightest of all metals. It is highly reactive and is used in batteries, alloys, and lubricants.
Mercury is a heavy, silvery-white metal that is liquid at room temperature. It is a poor conductor of heat and electricity and is used in thermometers, barometers, and other scientific instruments.
Lead is a heavy, soft, and malleable metal that is bluish-gray in color. It is a poor conductor of heat and electricity and is used in batteries, ammunition, and radiation shielding.
Silver is a white, lustrous metal that is a good conductor of heat and electricity. It is used in jewelry, coins, and silverware.