UPSC Prelims 2005 Q101: Science & Technology – Materials & Engineering
Which one of the following is the correct sequence of the given substances in the
decreasing order of their densities?
- (a) Steel > Mercury > Gold
- (b) Gold > Mercury > Steel
- (c) Steel > Gold > Mercury
- (d) Gold > Steel > Mercury
Answer: (b) Gold > Mercury > Steel
Explanation
Densities of gold, mercury and steel
| Substance | Approximate density |
|---|---|
| Gold | About 19.3 g/cm3 |
| Mercury | About 13.6 g/cm3 |
| Steel | About 7.8 g/cm3 |
In decreasing order of density the sequence is Gold > Mercury > Steel. This is why steel floats on liquid mercury while gold sinks in it.
Answer: (b) Gold > Mercury > Steel.
Why each option is right or wrong
- (a) Incorrect. Steel is less dense than mercury and gold.
- (b) CORRECT. Gold is densest, then mercury, then steel.
- (c) Incorrect. Steel cannot be denser than gold and mercury.
- (d) Incorrect. Steel is less dense than mercury.
Key point
Gold 19.3 > mercury 13.6 > steel 7.8 g/cm3; iron floats on mercury.
Remember
Gold is denser than mercury, which is denser than steel.
Common mistakes
- Assuming a liquid metal must be less dense than a solid one.
- Putting steel above mercury because steel is hard.
- Forgetting that gold is about two and a half times denser than steel.
Exam tip
Iron and steel float on mercury, but gold sinks in it.
Sources
- NCERT Class IX Science — Matter in Our Surroundings
- CRC Handbook of Chemistry and Physics — Densities of the elements (gold, mercury, iron)