UPSC Prelims 2008 Q116: Science & Technology – Chemistry
Which one of the following pairs of metals constitutes the lightest metal and the heaviest
metal, respectively?
- (a) Lithium and mercury
- (b) Lithium and osmium
- (c) Aluminium and osmium
- (d) Aluminium and mercury
Answer: (b) Lithium and osmium
Explanation
Lightest and heaviest metals
Among all known metallic elements, two specific ones hold the extremes of density.
| Option | Verdict | Reason |
|---|---|---|
| (a) Lithium and mercury | Incorrect | Lithium is indeed the lightest metal, but mercury is not the heaviest |
| (b) Lithium and osmium | Correct | Lithium is the lightest metal, and Osmium is the heaviest metal (by density) |
| (c) Aluminium and osmium | Incorrect | Aluminium is not the lightest metal; Lithium is lighter |
| (d) Aluminium and mercury | Incorrect | Neither is correctly the extreme-density metal here |
Lightest and heaviest metals:
| Point | Detail |
|---|---|
| Lightest metal | Lithium |
| Heaviest metal (by density) | Osmium |
Answer: (b) Lithium and osmium.
Why each option is right or wrong
- (a) Incorrect. Mercury is a dense liquid metal, but it is NOT the heaviest metal by density — Osmium is.
- (b) CORRECT. Lithium (lightest) and Osmium (heaviest) are the correct pair.
- (c) Incorrect. Aluminium is not the lightest metal; Lithium is lighter.
- (d) Incorrect. Neither metal here correctly represents the density extremes.
Key point
Lithium is the lightest metal, and Osmium is the heaviest metal by density — not mercury, which despite being a dense liquid metal, is not the heaviest.
Remember
Lithium and Osmium: the lightest and heaviest metals, respectively.
Common mistakes
- Confusing mercury's liquid-state density with being the overall heaviest solid metal (Osmium holds that distinction).
- Not knowing Lithium's status as the lightest metal.
- Mixing up Aluminium's relatively low density with being the absolute lightest metal.
Exam tip
Lightest metal = Lithium. Heaviest metal (by density) = Osmium. Mercury, despite its density, is not the heaviest.
Sources
- Encyclopaedia Britannica — lithium
- Encyclopaedia Britannica — osmium