Most harmful environmental pollutants are

Options

A. biodegradable
B. corrosive agents
C. non-biodegradable chemicals
D. All of the above

Answer

### Step-by-Step Solution:

1. **Understanding Pollutants**: Start by defining what environmental pollutants are. Environmental pollutants are substances that cause harm to the environment and living organisms.

2. **Types of Pollutants**: Identify the different types of pollutants. They can be categorized into biodegradable and non-biodegradable pollutants.

3. **Biodegradable Pollutants**: Discuss biodegradable pollutants. These are substances that can be decomposed by bacteria or other living organisms. Examples include human and animal waste. Since they can be broken down, they generally do not contribute significantly to long-term environmental pollution.

4. **Corrosive Agents**: Next, consider corrosive agents. These are typically strong acids or bases, such as hydrochloric acid or sulfuric acid. While they can be harmful, they do not fall under the category of persistent environmental pollutants.

5. **Non-Biodegradable Chemicals**: Now focus on non-biodegradable pollutants. These are substances that cannot be broken down in the environment. Examples include certain pesticides, heavy metals like lead and mercury, and radioactive waste. These substances can accumulate in the environment and are known to cause significant harm to living organisms, particularly through processes like biomagnification.

6. **Conclusion**: Based on the analysis, conclude that the most harmful environmental pollutants are non-biodegradable chemicals. Therefore, the correct answer to the question is option three: non-biodegradable substances.