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 determine the correct statement from the options provided, let's analyze each statement step by step.

### Step 1: Analyze Statement A
**Statement A:** "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 automobile combustion, but it is not a major component in the formation of photochemical smoke. The primary pollutants contributing to photochemical smoke are nitrogen oxides (NOx) and volatile organic compounds (VOCs), which react in the presence of sunlight to form ozone. Therefore, this statement is **false**.

### Step 2: Analyze Statement B
**Statement B:** "Classical smoke has an oxidizing character while the photochemical smoke is reducing in character."

- **Analysis:** This statement is incorrect. Classical smoke, often associated with the burning of fossil fuels, contains high levels of sulfur dioxide (SO2) and particulate matter, which can have a reducing character. In contrast, photochemical smoke, which occurs during sunny conditions and involves the reaction of sunlight with pollutants like NOx and VOCs, is characterized by the presence of ozone (O3), which is an oxidizing agent. Therefore, this statement is **false**.

### Step 3: Analyze Statement C
**Statement C:** "During formation of smoke, the level of ozone in the atmosphere goes down."

- **Analysis:** This statement is also incorrect. Ozone is a primary component of photochemical smoke. During the formation of photochemical smoke, ozone levels actually increase due to the photochemical reactions involving NOx and VOCs. Thus, this statement is **false**.

### Step 4: Analyze Statement D
**Statement D:** "The major role of oxides of nitrogen."

- **Analysis:** This statement is true. Nitrogen oxides (NOx) are indeed major contributors to the formation of photochemical smoke. They react with volatile organic compounds in the presence of sunlight to produce ozone, which is a key component of photochemical smog. Therefore, this statement is **true**.

### Conclusion
The correct statement among the options provided is that nitrogen oxides play a major role in photochemical smoke formation.

### Final Answer
The correct statement is: "The major role of oxides of nitrogen."

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