Question

According to Central Pollution Control Board (CPCB), particulate matter of which size is responsible for causing the greatest harm to humans?

• A. \(2.5\ \mu \text{m}\) or less in diameter.
• B. \(4.5\ \mu \text{m}\) or more in diameter.
• C. \(5\ \mu \text{m}\) to \(7\ \mu \text{m}\) in diameter
• D. \(10\ \mu \text{m}\) or more in diameter.

Hint:

Fine particles that reach deep into the lungs are the most harmful.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
The Central Pollution Control Board identifies fine particulate matter of diameter \(2.5\ \mu\text{m}\) or less (PM 2.5) as the most harmful to human health.

Step 2: Why harmful
Such particles pass deep into the lungs up to the alveoli and cause breathing trouble, irritation, inflammation, lung damage and early death.

Step 3: Conclusion
Coarser particles are mostly trapped in the nose and upper airways. So the most harmful particles are \(2.5\ \mu\text{m}\) or less in diameter.

Final Answer:
Particles of 2.5 micrometre diameter or less are the most harmful. \[ \boxed{\text{(A) }2.5\ \mu\text{m or less in diameter}} \]