Question

According to Central Pollution Control Board, which particulate matter size in diameter (in micrometers) are responsible for causing the greatest harm to human health?

• A. 2.5 or less
• B. 2.5 to 5.0
• C. 5.0 to 7.5
• D. 7.5 to 10

Hint:

The smaller the particle, the deeper it reaches into the lungs.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
The Central Pollution Control Board identifies fine particles of diameter \( 2.5 \) micrometres or less (PM 2.5) as the most harmful to health.

Step 2: Why they are harmful
Being so small, they are not filtered out in the nose and throat. They reach deep into the lungs and cause irritation, inflammation, breathing problems and lung damage.

Step 3: Conclusion
Larger particles are mostly trapped in the upper airways, so the most harmful size is \( 2.5 \) micrometres or less.

Final Answer:
Particles of 2.5 micrometres or less are the most harmful. \[ \boxed{\text{(A) }2.5 \text{ or less}} \]