According to the central pollution control Board PM 2.5 are responsible for causing the greatest harm to human health. PM 2.5 stands for

Options

A. Particulate matter which are 2.5 micrometers or less in diameter
B. Particulate matter which are 2.5 micrometers or more in diameter
C. Particulate matter which are 2.5 nanometers or less in diameter
D. Particulate matter which are 2.5 nanometers or more in diameter

Answer

To solve the question regarding what PM 2.5 stands for, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Context**: The question refers to PM 2.5 and its impact on human health as stated by the Central Pollution Control Board (CPCB). PM 2.5 is a term commonly used in discussions about air quality and pollution.

**Hint**: Look for the context in which PM 2.5 is mentioned. It is related to air pollution and health effects.

2. **Defining PM**: PM stands for "Particulate Matter." This is a term used to describe tiny particles or droplets in the air that can be inhaled and cause health problems.

**Hint**: Think about what "PM" could represent in environmental science, especially in relation to air quality.

3. **Understanding the Measurement**: The "2.5" in PM 2.5 refers to the size of the particulate matter. Specifically, it indicates that these particles are 2.5 micrometers or less in diameter. This size is significant because particles of this size can penetrate deep into the lungs and even enter the bloodstream.

**Hint**: Consider the implications of the size of particles on health. Smaller particles can have more severe effects.

4. **Health Implications**: PM 2.5 is known to cause various health issues, including respiratory problems and cardiovascular diseases. This is why it is highlighted as a major pollutant by organizations like the CPCB.

**Hint**: Reflect on why certain sizes of particulate matter are more harmful than others.

5. **Conclusion**: Therefore, PM 2.5 stands for "Particulate Matter" with a diameter of 2.5 micrometers or less.

**Hint**: Summarize your findings to arrive at the final answer.

### Final Answer:
PM 2.5 stands for "Particulate Matter" that is 2.5 micrometers or less in diameter.