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Topic Photochemical smog
Asked 3 times across 3 UPSC exams over 12 years (2013–2025), peaking in 2013.
Key insights
- Most tested in CSE — 1 of 3 PYQs
- Most asked in 2013
- Recurs across 3 years (2013–2025)
How it travelled across exams
First appearance in each exam — the same idea, reframed.
CSE 2013 → GEO 2024 → EPFO 2025
How the concept evolved
Rising — more than half its appearances (2 of 3) are since 2016.
Related concepts
Ideas UPSC tests alongside this one — keep exploring.
Sample questions
You've seen the pattern — here are a few of the actual PYQs.
EPFO2025
Which one among the following are the primary reactants of photochemical smog ?
- A Sulphur Hexafluoride and Soot
- B Carbon Monoxide and Ozone
- C Nitric Oxide and Unburnt Hydrocarbons
- D Peroxy Radicals and Sub-oxides
Answer key not yet available (pending official release)
Environment & Ecology › Pollution & Waste
GEO2024
Which of the following statements about Photochemical Smog is/are correct ?
- It irritates the eyes
- It leads to cracking of rubber
- It causes considerable damage to plant life. Select the answer
using the code given below :
- A 1, 2 and 3 ✓
- B 2 and 3 only
- C 1 and 2 only
- D 3 only
✓ Correct answer: (A)
Environment & Ecology › Pollution & Waste
CSE2013
Photochemical smog is a resultant of the reaction among
- A NO2, O3 and peroxyacetyl nitrate in the presence of sunlight ✓
- B CO, O2 and peroxyacetyl nitrate in the presence of sunlight
- C CO, CO2 and NO2 at low temperature
- D high concentration of NO2, O3 and CO in the evening
✓ Correct answer: (A)
Environment & Ecology › Pollution & Waste
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