2015 GS Paper I, all questions

UPSC Prelims 2015 · GS Paper I

Question 93: Science and Technology

With reference to bio-toilets used by the Indian Railways, consider the following statements :

  1. 1.The decomposition of human waste in the bio-toilets is initiated by a fungal inoculum.
  2. 2.Ammonia and water vapour are the only end products in this decomposition which are released into the atmosphere.

Which of the statements given above is/are correct?

a1 only
b2 only
cBoth 1 and 2
dNeither 1 nor 2

AnswerUPSC’s answer is (d).

Railway bio-toilets, developed with DRDO, use anaerobic bacteria to decompose human waste, not a fungal inoculum, so statement 1 is wrong. The waste is broken down into water and gases, mainly methane and carbon dioxide, so ammonia and water vapour are not the only end products, and statement 2 is wrong. Remember: bacteria in, methane and carbon dioxide out.

  • 1. The decomposition is begun by anaerobic bacteria, not fungi.
  • 2. The end products include methane and carbon dioxide, not only ammonia and water vapour.

How you could have got this

  1. If you were sure statement 2 is not correct, (b) and (c) go: each of them includes 2.

    What you needed to know: The end products include methane and carbon dioxide, not only ammonia and water vapour.

    The red flag in statement 2 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 not correct, (a) goes: it includes 1.

    What you needed to know: The decomposition is begun by anaerobic bacteria, not fungi.

Only (d) is left. This one needs every statement.

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) Wrong: the inoculum consists of anaerobic bacteria, not fungi.
  • (b) Wrong: methane and carbon dioxide are also released.
  • (c) Wrong: both statements are false.
  • (d) Correct: neither statement is correct.

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

Practise this paper timedPrevious questionNext question

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