Q.12 Which of the following statements is INCORRECT?
- AIncomplete combustion of carbonaceous fuels releases carbon dioxide as the major pollutant.Correct
- BMunicipal drainage systems emit H2S gas.
- CThermal power houses are the main contributors to SO₂ emissions.
- DWelding operations may release nitrogen oxide.
Solution
Concept
Incomplete combustion of carbon fuels mainly produces carbon monoxide (CO), not CO₂.
Formula
Complete: C + O₂ → CO₂ ; Incomplete: 2C + O₂ → 2CO
Step-by-step solution
1. Complete combustion of carbon gives CO₂. 2. When oxygen is not enough (incomplete combustion), carbon gives CO. 3. So the major pollutant from incomplete combustion is CO, and statement A is wrong. 4. Sewers produce H2S by anaerobic decomposition, so B is correct. 5. Coal-based thermal power plants are the largest source of SO₂, so C is correct. 6. The high temperature of welding arcs forms NOx, so D is correct.
Explanation
When fuel burns with too little oxygen, it forms carbon monoxide (CO), which is a toxic gas. CO₂ is the product of complete combustion. So statement A is the incorrect one.
Why the other options are wrong
B: True. Anaerobic decay of sewage gives H2S. C: True. Sulphur in coal burnt in thermal plants gives SO₂. D: True. High-temperature welding arcs produce nitrogen oxides.
Shortcut
Incomplete combustion gives CO. Complete combustion gives CO₂.
Common mistake
Thinking CO₂ is the main product of incomplete combustion.
Correct answer: A) Incomplete combustion of carbonaceous fuels releases carbon dioxide as the major pollutant.