2013 GS Paper I, all questions
UPSC Prelims 2013 · GS Paper I
Question 49: Environment and Ecology
Photochemical smog is a resultant of the reaction among
aNO2, O3 and peroxyacetyl nitrate in the presence of sunlight
bCO, O2 and peroxyacetyl nitrate in the presence of sunlight
cCO, CO2 and NO2 at low temperature
dhigh concentration of NO2, O3 and CO in the evening
AnswerUPSC’s answer is (a).
Photochemical smog forms when sunlight acts on nitrogen oxides and hydrocarbons released by vehicles. This produces ozone, nitrogen dioxide and peroxyacetyl nitrate (PAN), which irritate the eyes and lungs. Sunlight is essential, so the smog forms in the daytime and in warm weather, not at low temperature or in the evening; carbon monoxide and carbon dioxide are not the key reactants.
Why each option is right or wrong
- (a) Correct. NO2, O3 and PAN form in sunlight.
- (b) Wrong. Carbon monoxide and oxygen are not the key reactants.
- (c) Wrong. Photochemical smog needs sunlight, not low temperature.
- (d) Wrong. Sunlight is needed, so it is a daytime process, not an evening one.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2013, General Studies Paper I, Series A. The paper on upsc.gov.in.