Question

Tropospheric ozone is an important ingredient of photochemical smog. London smog event was an example of oxidising smog formed by photochemical reaction in troposphere. Which of the following is most appropriate?

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

London smog (1952) = reducing/sulphurous smog (SO$_2$ + fog + coal smoke). Photochemical smog = oxidising smog (O$_3$, PAN, NOx + sunlight).

Answer 1

The Correct Option is C

Step 1: Concept
Types of air pollution: photochemical smog vs. London (sulphurous) smog.

Step 2: Meaning
Photochemical smog (Los Angeles type) involves tropospheric ozone and NOx in sunlight. London smog (1952) was a reducing smog from coal combustion in cold, foggy conditions.

Step 3: Analysis
Statement (A) is correct: tropospheric ozone is a key component of photochemical smog.
Statement (R) is incorrect: the 1952 London smog was a reducing (sulphurous) smog, not photochemical smog. It was caused by SO$_2$ and particulates from coal combustion --- not by photochemical reactions forming ozone.

Step 4: Conclusion
(A) is correct; (R) is incorrect. Final Answer: (C)