The correct answer is D. Sulphur-dioxide.
Sulphur-dioxide is a gas that is produced when fossil fuels such as coal and oil are burned. It is a major air pollutant that can cause a variety of health problems, including respiratory problems, heart disease, and cancer. Sulphur-dioxide can also damage crops and forests.
Carbon dioxide is a gas that is produced when plants and animals breathe. It is also produced when fossil fuels are burned. Carbon dioxide is not as harmful to human health as sulphur-dioxide, but it is a greenhouse gas that contributes to climate change.
Oxygen is a gas that is essential for life. It is not an air pollutant.
Nitrogen is a gas that makes up about 78% of the air. It is not an air pollutant.
Sulphur-dioxide is the most significant air pollutant because it is a major cause of respiratory problems, heart disease, and cancer. It can also damage crops and forests.