Question

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Smog refers to heavily polluted air that forms in cities during winter.
Reason (R) : It is the emission of CH$_4$ and aerosols from the burning of fossils.
In the light of the above statements, choose the most appropriate answer from the options given below :

• 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:

Classic Smog = Smoke + Fog + SO$_2$. It happens in Winter.
Photochemical Smog = Sunlight + NO$_x$ + VOCs. It happens in Summer.

Answer 1

The Correct Option is C

Concept: Smog (a portmanteau of smoke and fog) is a type of intense air pollution. Understanding its chemical composition is key to identifying its causes and types (Classical vs. Photochemical).

Step 1: Evaluate Assertion (A).
Assertion (A) is correct. "Classical" or London-type smog typically forms in cool, humid climates (winter) when smoke particles and sulfur dioxide from coal burning mix with fog. This is a common phenomenon in many industrialized cities during winter months.

Step 2: Evaluate Reason (R).
Reason (R) is incorrect. While aerosols are a component of smog, the primary gases involved in smog formation are sulfur dioxide ($SO_2$) for classical smog, or nitrogen oxides ($NO_x$) and volatile organic compounds ($VOCs$) for photochemical smog. Methane ($CH_4$) is a greenhouse gas but is not a primary component or direct cause of typical urban smog.

Step 3: Conclusion.
Since the assertion accurately describes the occurrence of smog but the reason provides an incorrect chemical explanation of its formation, Option (3) is the most appropriate choice.