Secondary pollutants is/are:-
(a) Brown air (b) Grey air
(c) Acid Rain (d) DDT

Options

A. a,b and c are correct
B. a and b are correct
C. b and d are correct
D. a and c are correct

Answer

To determine which of the options provided is a secondary pollutant, let's break down the definitions and characteristics of primary and secondary pollutants step by step.

### Step 1: Understand the Definitions
- **Primary Pollutants**: These are pollutants that are emitted directly from a source. Examples include carbon monoxide from vehicles, sulfur dioxide from industrial processes, and particulate matter from construction sites.
- **Secondary Pollutants**: These are not emitted directly. Instead, they form in the atmosphere through chemical reactions between primary pollutants and other atmospheric components.

### Step 2: Analyze Each Option
1. **Brown Air**: This term generally refers to a mixture of pollutants, including nitrogen oxides and particulate matter, which can lead to smog formation. It is not a specific chemical but rather a result of secondary reactions.

2. **Grey Air**: Similar to brown air, grey air is associated with particulate matter and sulfur dioxide, often resulting from industrial emissions. It also represents a mixture of pollutants rather than a specific secondary pollutant.

3. **Acid Rain**: This is a well-known secondary pollutant. It forms when sulfur dioxide and nitrogen oxides (primary pollutants) react with water vapor in the atmosphere, leading to the formation of sulfuric and nitric acids that fall as precipitation.

4. **DDT**: Dichloro-Diphenyl-Trichloroethane (DDT) is a synthetic pesticide that is considered a primary pollutant because it is directly introduced into the environment for pest control.

### Step 3: Identify the Correct Answer
From the analysis:
- **Brown Air** and **Grey Air** are not specific secondary pollutants but rather mixtures of pollutants.
- **Acid Rain** is a clear example of a secondary pollutant.
- **DDT** is a primary pollutant.

Thus, the correct answer is **(c) Acid Rain**.

### Final Answer
(c) Acid Rain

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