The correct answer is A. CO.
Nitrogen oxides (NOx) and hydrocarbons (HC) released by automobiles interact in the presence of sunlight to form photochemical smog. Photochemical smog is a mixture of air pollutants that are formed when sunlight reacts with emissions from cars, power plants, and other sources. The main components of photochemical smog are ozone (O3), nitrogen dioxide (NO2), and peroxyacetyl nitrate (PAN).
Ozone is a gas that can irritate the lungs and make it difficult to breathe. It can also damage plants and crops. Nitrogen dioxide is a gas that can cause respiratory problems and can also contribute to acid rain. PAN is a gas that can cause eye irritation and can also damage plants and crops.
Photochemical smog is a major air pollution problem in many cities around the world. It can cause a variety of health problems, including respiratory problems, heart problems, and cancer. It can also damage plants and crops.
CO is a colorless, odorless gas that is produced when gasoline is burned in an engine. It is a major air pollutant and can cause a variety of health problems, including headaches, dizziness, and nausea. It can also be fatal in high concentrations.
B. PAN is a secondary pollutant that is formed when nitrogen oxides and hydrocarbons react in the presence of sunlight. It is a major component of photochemical smog and can cause a variety of health problems, including eye irritation, respiratory problems, and headaches.
C. SO2 is a gas that is produced when sulfur-containing fuels are burned. It is a major air pollutant and can cause a variety of health problems, including respiratory problems, heart problems, and cancer. It can also damage plants and crops.
D. Aerosol is a suspension of fine solid particles or liquid droplets in the air. It can be formed from a variety of sources, including natural sources (such as volcanoes) and human activities (such as burning fossil fuels). Aerosols can contribute to air pollution and can also have a variety of health effects, including respiratory problems, heart problems, and cancer.