UPSC Prelims 2012 · GS Paper I
Question 13: Science and Technology
What is the role of ultraviolet (UV) radiation in the water purification systems?
- 1.It inactivates/kills the harmful microorganisms in water.
- 2.It removes all the undesirable odours from the water.
- 3.It quickens the sedimentation of solid particles, removes turbidity and improves the clarity of water.
Which of the statements given above is/are correct?
AnswerUPSC’s answer is (a).
Ultraviolet radiation disinfects water: it damages the genetic material of bacteria, viruses and other microorganisms, inactivating them without adding chemicals. It does not remove odours, and it does not settle suspended particles or reduce turbidity; coagulation, sedimentation and filtration do that. UV works best on clear water, because particles shield microbes from the light.
- 1. UV damages microbial DNA and so inactivates harmful organisms.
- 2. UV does not remove all odours; activated carbon and aeration deal with those.
- 3. Sedimentation and clarity come from coagulation and filtration, not UV.
How you could have got this
- If you were sure statement 3 is not correct, (b), (c) and (d) go: each of them includes 3.
What you needed to know: Sedimentation and clarity come from coagulation and filtration, not UV.
Only (a) is left. You didn’t need statements 1 or 2.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Correct: UV only inactivates or kills harmful microorganisms.
- (b) Wrong: UV does not remove odours or settle particles.
- (c) Wrong: UV does not quicken sedimentation or clear turbidity.
- (d) Wrong: statements 2 and 3 describe jobs UV does not do.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2012, General Studies Paper I, Series A. The paper on upsc.gov.in.