Explanation:

Carbon dioxide (CO2) is not considered a pollutant in normal circumstances.

Hydrocarbons:
- Hydrocarbons are organic compounds consisting of hydrogen and carbon atoms.
- They are released into the atmosphere as a result of incomplete combustion of fossil fuels, such as gasoline, diesel, and natural gas.
- Hydrocarbons are a major component of air pollution and contribute to the formation of smog and ground-level ozone, which are harmful to human health and the environment.

Carbon monoxide:
- Carbon monoxide (CO) is a colorless and odorless gas that is produced by the incomplete combustion of carbon-based fuels.
- It is primarily emitted from vehicles, industrial processes, and residential heating systems.
- Carbon monoxide is a pollutant as it can be toxic when inhaled in high concentrations. It reduces the ability of red blood cells to carry oxygen, leading to various health problems.

Sulphur dioxide:
- Sulphur dioxide (SO2) is a gas produced by the burning of fossil fuels that contain sulfur, such as coal and oil.
- It is one of the main contributors to acid rain and can cause respiratory problems, especially in individuals with asthma or other respiratory conditions.
- Sulphur dioxide emissions also contribute to the formation of particulate matter and can have detrimental effects on human health and ecosystems.

Carbon dioxide:
- Carbon dioxide (CO2) is a naturally occurring gas that is essential for life on Earth.
- It is produced through various natural processes, such as respiration, volcanic eruptions, and decomposition of organic matter.
- While carbon dioxide is a greenhouse gas and contributes to global warming, it is not considered a pollutant in normal circumstances.
- It is a naturally occurring component of the Earth's atmosphere and plays a crucial role in the carbon cycle and the regulation of Earth's temperature.

Therefore, among the given options, carbon dioxide (CO2) is not considered a pollutant in normal circumstances. It is the result of natural processes and is only considered a problem when its concentration in the atmosphere increases significantly due to human activities, such as the burning of fossil fuels.