Explanation:

- Water vapour: It's a natural component of the atmosphere. Typically, it isn't considered a pollutant and plays a role in the Earth's heat balance.

- Carbon dioxide (CO2): It's a significant greenhouse gas contributing to global warming and climate change. Considered an air pollutant due to its environmental impact.

- Hydrogen gas: Not typically considered an air pollutant. It's harmless and doesn't contribute to air quality issues like smog or climate change.

- Option:1) Only I - Water vapour isn't a harmful pollutant.

- Option:2) Only II - Carbon dioxide is a notable air pollutant.

- Option:3) Only III - Hydrogen gas doesn't pollute the air.

- Option:4) Both II and III - Hydrogen gas is not a pollutant.