UPSC CSE Prelims 2008
Lithium (Li) is the lightest known metal. It is the third element on the periodic table, possessing an exceptionally low density of 0.53 g/cm³, which makes it less dense than water.
Osmium (Os) is the densest naturally occurring metal, with a density of approximately 22.59 g/cm³. It is a hard, brittle, bluish-white transition metal, frequently utilized in alloys for applications demanding high durability.
Option (a) Lithium and mercury: While lithium is correctly identified as the lightest metal, mercury (density approximately 13.53 g/cm³) is not the heaviest. Osmium has a significantly higher density.
Option (c) Aluminium and osmium: Aluminium (density approximately 2.7 g/cm³) is a lightweight metal but is considerably denser than lithium. Osmium is correctly identified as the heaviest.
Option (d) Aluminium and mercury: This pair does not represent the lightest and heaviest metals, respectively. Aluminium is denser than lithium, and mercury is less dense than osmium.