2015 GS Paper I, all questions

UPSC Prelims 2015 · GS Paper I

Question 18: Environment and Ecology

With reference to 'fly ash' produced by the power plants using coal as fuel, which of the following statements is/are correct?

  1. 1.Fly ash can be used in the production of bricks for building construction.
  2. 2.Fly ash can be used as a replacement for some of the Portland cement contents of concrete.
  3. 3.Fly ash is made up of silicon dioxide and calcium oxide only, and does not contain any toxic elements.

Select the correct answer using the code given below.

a1 and 2
b2 only
c1 and 3
d3 only

AnswerUPSC’s answer is (a).

Fly ash, the fine ash from burning coal in power plants, is used in making bricks and as a partial replacement for Portland cement in concrete, so statements 1 and 2 are correct. It is not made only of silicon dioxide and calcium oxide: it also contains aluminium and iron oxides and traces of toxic heavy metals such as arsenic, lead and mercury, so statement 3 is wrong.

  • 1. Fly ash bricks are widely used in construction.
  • 2. Fly ash can replace part of the Portland cement in concrete.
  • 3. It also contains alumina, iron oxide and toxic heavy metals such as arsenic and lead.

How you could have got this

  1. If you were sure statement 3 is not correct, (c) and (d) go: each of them includes 3.

    What you needed to know: It also contains alumina, iron oxide and toxic heavy metals such as arsenic and lead.

    The red flag in statement 3 is “only”. In UPSC’s papers, statements with “only” were true 27% of the time (82 statements). A hint, not a rule.

  2. Then, if you were sure statement 1 is correct, (b) goes: it leaves 1 out.

    What you needed to know: Fly ash bricks are widely used in construction.

Only (a) is left. You didn’t need statement 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: bricks and cement replacement are real uses; fly ash also holds toxic elements.
  • (b) Incomplete: fly ash is also used for bricks.
  • (c) Wrong: statement 3 is false, as fly ash contains toxic elements.
  • (d) Wrong: statement 3 alone is false.

Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2015, General Studies Paper I, Series A. The paper on upsc.gov.in.