How can carbon dioxide be considered a pollutant when it is a natural component of air?

High levels of acts as pollutant in the atmosphere.

Explanation:

Carbon dioxide is a natural component of air. It is produced by the human body metabolism and by other factors. However, concentrations reaching above normal levels is considered to be as a pollutant.

Carbon dioxide is produced as a byproduct of many industrial and commercial chemical synthesis. This emission directly reaches in the air and causes high levels of concentration in the atmosphere.

High levels of causes greenhouse effect, acid rain as well as global warming and thus, it is considered to be as a pollutant.

The correct statement is a pure substance because it is a compound.

Explanation:

A pure substance is defined as the substance which is formed by same or different type of atoms which are chemically combined in a fixed ratio by mass. Compounds and elements are considered as pure substances.

Impure substances are defined as the substances which do not have definite chemical composition. They are basically mixtures of substances which are not chemically combined.

A compound is a substance which is formed by two or more different type of atoms when they chemically combine.

An element is defined as the substance which have only one type of atoms.

Emerald is a compound having chemical formula of . This is considered as a pure substance.

Hence, the correct statement is a pure substance because it is a compound.