Question

Identify the correct statements from the following
I. Photochemical smog has high concentration of oxidising agents
II. \(\text{NO}_2\) is present in classical smog
III. Higher concentration of \(\text{SO}_2\) in air can cause stiffness of flower buds
IV. pH of rain water is approximately 7.5

• A. I & III
• B. I & II
• C. III & IV
• D. II & III

Hint:

Contrast the two smogs: Classical = Cool + Humid + \(SO_2\) + Reducing. Photochemical = Warm + Sunny + \(NO_2/O_3\) + Oxidising.

Answer 1

The Correct Option is A

Step 1: Analyze Statement I:
Photochemical smog is also known as Oxidising Smog. It occurs in warm, dry, and sunny climates and contains oxidising agents like Ozone (\(\text{O}_3\)) and Peroxyacetyl nitrate (PAN). \(\rightarrow\) Statement I is Correct.
Step 2: Analyze Statement II:
Classical smog (London smog) occurs in cool, humid climates and is chemically reducing in nature. It consists of smoke, fog, and sulphur dioxide (\(\text{SO}_2\)). Nitrogen dioxide (\(\text{NO}_2\)) is a primary component of Photochemical smog, not classical smog. \(\rightarrow\) Statement II is Incorrect.
Step 3: Analyze Statement III:
High concentrations of \(\text{SO}_2\) affect plants. It causes chlorosis and specifically leads to the stiffness of flower buds, which eventually fall off from plants. \(\rightarrow\) Statement III is Correct.
Step 4: Analyze Statement IV:
Normal rain water has a pH of about 5.6 due to the dissolution of atmospheric \(\text{CO}_2\) forming carbonic acid. pH 7.5 would be alkaline, which rain water is typically not. Acid rain has pH<5.6. \(\rightarrow\) Statement IV is Incorrect. Conclusion:
Statements I and III are correct. Final Answer:
Option (A).