UPSC Prelims 1999 · General Studies
Question 127: Science and Technology
Consider the following statements: I. Glass can be etched or scratched by diamond. II. Glass can be etched or scratched by hydrofluoric acid. III. Glass can be etched or scratched by aqua regia. IV. Glass can be etched or scratched by concentrated sulphuric acid. Which of these statements are correct?
AnswerThe answer is (c).
Diamond, the hardest natural substance, scratches glass (I). Hydrofluoric acid reacts with the silica in glass and etches it, which is how glass is frosted (II). Aqua regia, a mixture of nitric and hydrochloric acids, attacks gold and platinum but not glass, and concentrated sulphuric acid does not etch glass either, so III and IV are incorrect. Remember: only diamond and hydrofluoric acid mark glass.
- I. Diamond is harder than glass and scratches it.
- II. Hydrofluoric acid attacks the silica in glass.
- III. Aqua regia does not etch glass.
- IV. Concentrated sulphuric acid does not etch glass.
Why each option is right or wrong
- (a) Wrong. IV is false.
- (b) Wrong. III is false and I is left out.
- (c) Right. I and II.
- (d) Wrong. IV is false and I is left out.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1999, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.