Question

Modern coal-based thermal power stations pollute the atmosphere by adding:

• A. NOX and SO2
• B. NOX, SO2 and SPM
• C. NOX, SO2, SPM and CO
• D. NOX, SO2 and CO

Hint:

Coal combustion mainly contributes to gaseous pollutants like NOX and SO2, along with particulate pollution in the form of ash and dust.

Answer 1

The Correct Option is B

Burning coal at high temperature does two things at once: it oxidizes atmospheric nitrogen into nitrogen oxides (NOx), and it burns off the sulfur impurities naturally present in coal into sulfur dioxide (SO2).
On top of these gases, the combustion also throws fine ash and unburnt particles into the air as suspended particulate matter (SPM), a very visible and well-documented pollutant from coal plants.
Modern plants are engineered for efficient combustion, so carbon monoxide, a sign of incomplete burning, isn't one of their defining pollutants the way NOx, SO2 and SPM are.
So the correct answer is NOx, SO2 and SPM.

Answer 2

We can also work through this by tracing each pollutant back to its physical source in coal combustion, and checking which set of sources is genuinely present:

1. NOx and SO2 only: Traces back correctly to nitrogen in the air (oxidized at high combustion temperature) and sulfur impurities in coal, but misses the physical ash residue that combustion inevitably produces.
2. NOx, SO2 and SPM: Adds the ash and unburnt fine particles thrown up during combustion (SPM) to the two gaseous sources, covering all three physical byproducts that coal burning genuinely generates in a thermal plant.
3. NOx, SO2, SPM and CO: Adds carbon monoxide, which specifically traces back to insufficient oxygen during combustion, something modern, well-controlled thermal stations are designed to avoid, so this source isn't characteristic of them.
4. NOx, SO2 and CO: Includes the incomplete-combustion byproduct CO while dropping the ash-residue byproduct SPM, mismatching what actually happens physically.

Tracing each candidate pollutant to a real physical source in the combustion process points to one specific combination.

Therefore, the correct answer is NOx, SO2 and SPM.