Question

Which of the following is not a pollutant?
A. ${\text{S}}{{\text{O}}_2}$
B. ${\text{C}}{{\text{O}}_2}$
C. ${\text{CO}}$
D. ${\text{N}}{{\text{O}}_2}$

Answer 1

Hint: Pollutants are substances or energy that are introduced into the normal environment and produce unwanted changes. Any types of foreign materials which causes undue effects on the environmental condition are termed as pollutants. They interfere with the normal atmospheric conditions.

Complete answer:
A pollutant can be defined as any element, material or substances that create an undue effect on the atmospheric conditions. Pollutants cause harmful effects on the biological flora and fauna once they are emitted into the atmosphere. Many pollutants enter into the atmosphere through different pathways and cause harmful effects.
Carbon dioxide is naturally produced by animals and humans as a byproduct of metabolic activities. It is one of the greenhouse gases and is responsible for maintaining the temperature of the atmosphere. The plants take in ${\text{C}}{{\text{O}}_2}$ and use it as an important element in the photosynthetic process. Nitrogen oxides (${\text{N}}{{\text{O}}_2}$) are poisonous highly reactive gases that are released into the atmosphere when fuel is burnt at high temperature. These gases are also emitted by vehicles, power plants, industrial boilers and turbines. Nitrogen oxide induces problematic chemical reactions into the atmosphere with volatile organic compounds. They are one of the chief pollutants and produce smog.
Sulphur oxides (${\text{S}}{{\text{O}}_2}$) contains both sulphur and oxygen molecules which are a group of pollutants that are responsible for acid rain. It readily dissolves in water and forms sulfurous acid or sulfuric acid which is the main component of acid rain. Major source of emission of sulphur oxides are the fuels which produce sulphur upon combustion. Other sources include power plants which burn high Sulphur coal as well as vehicles.
Carbon monoxide( ${\text{CO}}$) is produced from the incomplete combustion of fuels such as propane, natural gas, oil coal, wood. Carbon monoxide causes serious health problems as it reduces the ability of oxygen carrying capacity of the blood. It is emitted through furnaces, water heaters and fuel burning appliances.

Hence, the correct answer is option (B).

Note: Among the various gases, ${\text{C}}{{\text{O}}_2}$ is produced naturally and is involved in various environmental processes. Carbon dioxide is produced by the living organisms as a by-product of the various metabolic pathways and is released through exhalation by the animals and humans. Plants utilize ${\text{C}}{{\text{O}}_2}$ to produce carbohydrates and so, ${\text{C}}{{\text{O}}_2}$ is not considered as a pollutant when present within optimum levels.