The correct answer is option 2: Only II. Carbon dioxide is considered an air pollutant because it contributes to climate change and global warming. Water vapor, on the other hand, is a natural component of the Earth`s atmosphere and is not considered a pollutant. Hydrogen gas is also not an air pollutant as it is a clean and non-toxic gas. It is important to distinguish between natural components of the atmosphere and pollutants that are harmful to human health and the environment.