Which one of the following pairs of metals constitutes the lightest metal and the heaviest metal, respectively?

1. The question asks for the pair of metals constituting the lightest metal (lowest density) and the heaviest metal (highest density). 2. Lightest metal: Lithium (Li) has the lowest density among all metals (0.534 g/cm³). 3. Heaviest metal: Osmium (Os) has the highest density among all known elements (22.59 g/cm³), slightly denser than Iridium. 4. Aluminium has a low density but higher than Lithium. Mercury is dense but significantly less dense than Osmium. 5. Therefore, the correct pair is Lithium and osmium.