Question

Correct statement about photo-chemical smog is:

• A. It occurs in humid climate.
• B. It is a mixture of smoke, fog and SO2.
• C. It is reducing smog.
• D. It results from reaction of unsaturated hydrocarbons

Answer 1

The Correct Option is D

Let's analyze the question about photo-chemical smog, which is a common topic in environmental chemistry. The question asks us to identify the correct statement about photo-chemical smog from the given options.

Photo-chemical smog, also known as "Los Angeles smog," predominantly occurs in urban areas during warm, sunny conditions. It is formed by the reaction of sunlight with pollutants like nitrogen oxides (NO_x) and volatile organic compounds (VOCs), such as unsaturated hydrocarbons, present in the atmosphere. The reaction produces a mixture of various secondary pollutants, including ozone (O₃), which is a major component of photo-chemical smog.

1. Option 1: "It occurs in humid climate."
   This statement is incorrect. Photo-chemical smog typically develops in dry, sunny conditions rather than humid climates.
2. Option 2: "It is a mixture of smoke, fog, and SO₂."
   This description fits more with "London smog" or "classical smog," which is composed mainly of smoke, fog, and sulfur dioxide (SO₂). Therefore, this option is incorrect for photo-chemical smog.
3. Option 3: "It is reducing smog."
   This is again a characteristic of "classical smog," which contains reducing agents such as sulfur dioxide. Photo-chemical smog is oxidative in nature, leading to increased levels of ozone. Hence, this option is incorrect.
4. Option 4: "It results from the reaction of unsaturated hydrocarbons."
   This statement accurately describes photo-chemical smog. It results from the sunlight-initiated reaction of unsaturated hydrocarbons and nitrogen oxides in the atmosphere. Thus, this is the correct option.

Based on the above analysis, the correct answer is Option 4: "It results from the reaction of unsaturated hydrocarbons."