Question

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Photochemical smog causes cracking of rubber.
Reason (R) : Presence of ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate in photochemical smog makes it oxidizing.
Choose the most appropriate answer from the options given below :

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

Hint:

Remember the key features of photochemical smog: it is also called "oxidizing smog". Its main harmful components are ozone (O\(_3\)), peroxyacetyl nitrate (PAN), aldehydes, and nitrogen oxides. Ozone is responsible for the cracking of rubber and damage to vegetation. PAN and aldehydes cause severe eye irritation.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
We need to evaluate the validity of both the Assertion and the Reason, and then determine if the Reason correctly explains the Assertion. The topic is the chemical nature and effects of photochemical smog.
Step 2: Analysis of Assertion (A):
The Assertion states that photochemical smog causes the cracking of rubber. Photochemical smog contains high concentrations of ozone (O\(_3\)). Ozone is a very strong oxidizing agent and is known to attack the carbon-carbon double bonds present in the polymer chains of natural and synthetic rubbers (like polyisoprene). This chemical reaction, known as ozonolysis, breaks the polymer chains, leading to a loss of elasticity and the formation of cracks. Therefore, the Assertion (A) is true.
Step 3: Analysis of Reason (R):
The Reason lists the main components of photochemical smog: ozone (O\(_3\)), nitric oxide (NO), acrolein, formaldehyde, and peroxyacetyl nitrate (PAN). It states that these components make the smog oxidizing in nature. This is correct. Ozone, nitrogen dioxide (formed from NO), and PAN are all powerful oxidizing agents. This strong oxidizing character is the defining chemical property of photochemical smog. Therefore, the Reason (R) is true.
Step 4: Linking Reason and Assertion:
The Assertion states an effect (cracking of rubber), and the Reason states a fundamental property of the smog (it is oxidizing due to its components). The cracking of rubber is a process of oxidative degradation. It is precisely because photochemical smog is highly oxidizing (due to the presence of ozone, etc., as mentioned in the Reason) that it is able to attack and break down rubber molecules. Thus, the Reason provides the correct scientific explanation for the Assertion.
Step 5: Final Answer:
Both Assertion (A) and Reason (R) are true statements, and Reason (R) is the correct explanation for Assertion (A). This corresponds to option (A).