Read the below statements marked as Assertion (A) and Reason (R). Mark the correct options: Assertion (A): PM2.5 is more harmful than PM10 in AQI. Reason (R): PM2.5 particles are smaller and can reach deep into the lungs and bloodstream.

Correct — A. A is true. PM2.5 does more harm than PM10, and India's AQI builds that in: PM2.5 hits the top of the Satisfactory band at 60 µg/m³, PM10 only at 100 µg/m³.

R is true. PM2.5 particles are 2.5 micrometres across or less, small enough to pass deep into the lungs and into the bloodstream.

That small size is why PM2.5 is more harmful, so R explains A → option (a).

Why the others are wrong

• (b)
  Both A and R are true, but R is not the correct explanation of A. — R is the explanation, not a side fact. Particle size is exactly what makes PM2.5 more dangerous, so 'both true, not the explanation' drops the link.
• (c)
  A is true, but R is false. — R is true. Fine particles do penetrate deep into the lungs and can enter the bloodstream, so calling R false misreads the science.
• (d)
  A is false, but R is true. — A is true. India's AQI reaches each band at a lower PM2.5 concentration than PM10, because PM2.5 is the more harmful of the two.

Particulate matter is named by particle diameter: PM10 is 10 micrometres or less, PM2.5 is 2.5 micrometres or less.

Coarser particles tend to be caught in the nose and upper airways. Fine particles slip past, lodge deep in the lungs, and some cross into the blood.

That is why the index is stricter on PM2.5: the same AQI band is reached at a lower concentration.

Key facts

• PM2.5 is particulate matter 2.5 micrometres or less in diameter, and PM10 is 10 micrometres or less.
• India's AQI rates PM2.5 Satisfactory up to 60 µg/m³ but PM10 up to 100 µg/m³, both as 24-hour averages.
• The National AQI covers eight pollutants: PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃ and Pb.
• The overall AQI is the worst of the pollutant sub-indices.

Common traps

• Marking (b) because both statements sound true: ask whether R gives the reason for A, and here it does.
• Assuming the larger PM10 particle is more harmful because it is bigger.

No directly related past PYQ was found.