Multiple choice general knowledge Which of the following is the lightest metal? Mercury Silver Lithium Lead Reveal answer Fill a bubble to check yourself C Correct answer Explanation Lithium is the lightest metal with an atomic mass of approximately 6.94 u. Mercury is liquid at room temperature, silver is much denser (107.87 u), and lead is very heavy (207.2 u). Lithium is so light it floats on water.