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RAS question

Particulate Matter PM2.5 refers to particles with diameter less than:

Correct answer: (B) 2.5 micrometers.

PM2.5 refers to fine particulate matter made up of airborne particles less than 2.5 micrometres in diameter.

  1. (A)

    10 micrometers

  2. (B)

    2.5 micrometers

  3. (C)

    25 micrometers

  4. (D)

    2.5 millimeters

Explanation

PM2.5 is the fine fraction of particulate matter: particles with a diameter below 2.5 micrometres. The World Health Organization supports this definition and explains why size matters. PM10, at below 10 micrometres, can be inhaled and collect in the respiratory system, but PM2.5 is smaller and therefore more dangerous because it can lodge deep in the lungs and enter the bloodstream. That is why the exam links PM2.5 with respiratory and cardiovascular disease risk. Common sources relevant to Indian air-pollution questions include vehicles, power plants, construction activity and crop burning.

Why the other options are wrong

  • (A) 10 micrometres describes PM10, a coarser particulate category, not PM2.5.
  • (C) 25 micrometres is far larger than the fine-particle cut-off used for PM2.5.
  • (D) PM2.5 is measured in micrometres, so 2.5 millimetres is the wrong unit and a much larger size.

Concept

This tests the Environment and Ecology concept of air pollutants, especially particulate-matter classification by particle size. It recurs in RAS because PM2.5 connects basic definitions with health impacts, pollution sources and public-policy control measures.

Source

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