Pick up the correct statement :

Options

A. CO which is a major pollutant resulting from the combustion of fuels in automobiles plays a major role in photochemical smog
B. Classical smog has an oxidizing character while the photochemical smog is reducing in character
C. Photochemical smog occurs in day time whereas the classical smog occurs in the moming hours
D. During formation of smog the level of ozone in the atmosphere goes down

Answer

To solve the question of identifying the correct statement regarding environmental chemistry, we will analyze each of the four statements provided.

### Step 1: Analyze Statement 1
**Statement 1:** CO, which is a major pollutant resulting from the combustion of fuels in automobiles, plays a major role in photochemical smoke.

- **Analysis:** Carbon monoxide (CO) is indeed a pollutant from fuel combustion, but it is not the major contributor to photochemical smoke. Photochemical smoke is primarily formed from nitrogen oxides (NOx) and volatile organic compounds (VOCs) reacting in the presence of sunlight. Therefore, this statement is **incorrect**.

### Step 2: Analyze Statement 2
**Statement 2:** Classical smoke has an oxidizing character, while photochemical smoke has a reducing character.

- **Analysis:** Classical smoke, which is produced from the burning of fossil fuels, typically has a reducing character due to the presence of sulfur oxides and carbon particles. Photochemical smoke, on the other hand, has an oxidizing character due to the presence of ozone and other oxidants formed during the photochemical reactions. Thus, this statement is also **incorrect**.

### Step 3: Analyze Statement 3
**Statement 3:** Photochemical smoke occurs in daytime, whereas classical smoke occurs in the morning hours.

- **Analysis:** Photochemical smoke is indeed formed during the day when sunlight is available to drive the reactions between nitrogen oxides and VOCs. Classical smoke is more prevalent in the early morning hours when temperatures are lower and emissions from heating are higher. Therefore, this statement is **correct**.

### Step 4: Analyze Statement 4
**Statement 4:** During the formation of smoke, the level of ozone in the atmosphere goes down.

- **Analysis:** In the formation of photochemical smoke, ozone is produced as a secondary pollutant. However, it can also be consumed in reactions with nitrogen oxides, leading to a decrease in ozone levels in certain conditions. The statement is somewhat misleading but can be interpreted as correct in the context of photochemical reactions consuming ozone. Thus, this statement is **correct**.

### Conclusion
Based on the analysis:
- **Correct Statements:** Statement 3 and Statement 4.
- **Incorrect Statements:** Statement 1 and Statement 2.

### Final Answer
The correct statements are:
- Statement 3: Photochemical smoke occurs in daytime, whereas classical smoke occurs in the morning hours.
- Statement 4: During the formation of smoke, the level of ozone in the atmosphere goes down.