1. Which of the following correctly pairs a combustible element found in boiler fuels with the compound it forms during complete combustion with oxygen?
- A. Hydrogen reacts with oxygen to form water vapour (H2O)
- B. Carbon reacts with oxygen to form carbon monoxide (CO)
- C. Sulfur reacts with oxygen to form sulfur trioxide (SO3)
- D. Nitrogen reacts with oxygen to form nitrogen dioxide (NO2)
Show the answer and explanation
Answer: A. The three combustible elements in boiler fuels are carbon, hydrogen, and sulfur. During complete combustion, hydrogen combines with oxygen to produce water vapour (H2O). Carbon forms carbon dioxide (CO2), not carbon monoxide, which is an incomplete combustion product. Sulfur forms sulfur dioxide (SO2), not sulfur trioxide. Nitrogen is not a combustible element and its presence in air is generally treated as non-reactive at normal combustion temperatures.
Why the other options are not the answer
- B. Carbon monoxide is a product of incomplete combustion; complete combustion of carbon forms CO2.
- C. Complete combustion of sulfur forms sulfur dioxide (SO2), not sulfur trioxide.
- D. Nitrogen is not one of the combustible elements in boiler fuel (those are carbon, hydrogen and sulfur).