UPSC Prelims 2003 Q29: Science & Technology – Chemistry
Which one of the following statements is correct?
- (a) Liquid sodium is employed as a coolant in nuclear reactors
- (b) Calcium carbonate is an ingredient of toothpaste
- (c) Bordeaux mixture consists of sodium sulphate and lime
- (d) Zinc amalgams are used as a dental filling
Answer: (a) Liquid sodium is employed as a coolant in nuclear reactors
Explanation
> Note for students: Statement (b) 'calcium carbonate is an ingredient of toothpaste' is also factually true, so two options are right. The published key is (a); choose (a).
Facts about metals and compounds
| Statement | Verdict |
|---|---|
| a. Liquid sodium is used as a coolant in nuclear reactors | True — in fast breeder reactors |
| b. Calcium carbonate is an ingredient of toothpaste | Also true, as a mild abrasive |
| c. Bordeaux mixture is sodium sulphate and lime | False: it is copper sulphate and lime |
| d. Zinc amalgam is a dental filling | False: the dental amalgam is of silver, mercury and tin |
Statement (a) is correct: liquid sodium carries heat out of fast reactors. Statements (c) and (d) are false, and (b) is also a true statement, so the question has two true options.
Answer: (a) Liquid sodium is employed as a coolant in nuclear reactors.
Why each option is right or wrong
- (a) CORRECT. Liquid sodium is a coolant in fast breeder reactors.
- (b) Incorrect. It is also a true statement, but (a) is the published answer.
- (c) Incorrect. Bordeaux mixture is copper sulphate with lime.
- (d) Incorrect. Dental amalgam uses silver, not zinc.
Key point
Bordeaux mixture: CuSO4 + Ca(OH)2, a fungicide. Dental amalgam: Hg with Ag and Sn.
Remember
Liquid sodium is the coolant in fast breeder reactors.
Common mistakes
- Taking Bordeaux mixture as sodium sulphate and lime.
- Believing zinc amalgam is used in teeth.
- Forgetting liquid sodium's use in fast reactors.
Exam tip
Liquid sodium: good heat conductor, used in the FBTR at Kalpakkam.
Sources
- NCERT Class XI Chemistry — The s-Block Elements (sodium: uses)
- Encyclopaedia Britannica — sodium