UPSC Prelims 2004 Q127: Science & Technology – Materials & Engineering
Standard 18 - carat gold sold in the market contains
- (a) 82 parts gold and 18 parts other metals
- (b) 15 parts gold and 82 parts other metals
- (c) 18 parts gold and 6 parts other metals
- (d) 9 parts gold and 15 parts other metals
Answer: (c) 18 parts gold and 6 parts other metals
Explanation
Composition of 18-carat gold
| Quantity | Value |
|---|---|
| Pure gold | 24 carat = 24 parts of gold |
| 18-carat gold | 18 parts gold and 6 parts other metals (75% gold) |
| Other metals | Usually copper and silver for hardness |
In 18-carat gold, 18 of the 24 parts are gold and the remaining 6 parts are other metals, so it is 75% pure.
Answer: (c) 18 parts gold and 6 parts other metals.
Why each option is right or wrong
- (a) Incorrect. 82 and 18 parts do not total 24 parts.
- (b) Incorrect. 15 parts of gold and 82 parts other metals is meaningless.
- (c) CORRECT. 18 parts gold and 6 parts other metals.
- (d) Incorrect. 9 parts of gold would be 9-carat.
Key point
Carat n means n parts of gold in 24 parts; so 22 carat gold is 91.6 percent gold.
Remember
18-carat gold is 75 percent gold.
Common mistakes
- Taking 18 as the percentage of gold.
- Forgetting that pure gold is 24 carat.
- Mixing carat of gold with the carat weight of diamonds.
Exam tip
The carat number divided by 24 gives the gold fraction.
Sources
- Bureau of Indian Standards — IS 1417: Gold and gold alloys, jewellery/artefacts — Fineness and marking
- Encyclopaedia Britannica — carat