Which of the following is NOT a pollutant gas released during fuel combustion?

The correct answer is helium, as it is not a pollutant gas released during fuel combustion. When fuels burn, they typically undergo a chemical reaction with oxygen that produces various gases as by-products.

Carbon dioxide is a common product of combustion; it is released when carbon-containing fuels are burned, contributing to greenhouse gas emissions. Water vapour, while often considered a natural component of the atmosphere, is also produced during combustion and can contribute to atmospheric moisture and climate effects. Sulfur dioxide is produced when sulfur-containing fuels are burned, and it is known for its role in air pollution and acid rain formation.

Helium, on the other hand, is a noble gas that does not form compounds easily and is not generated in significant quantities during fuel combustion. Its inert nature means it does not react with other substances in the way that combustion gases do, making it distinct from the other gases listed.