Which is a pure substance

Subject : Chemistry

Question: Which is a pure substance?

A) soda

B) gasoline

C) salt water

D) carbon dioxide

Expert Verified Solution:

The correct answer is:

Carbon dioxide

Explanation:

A pure substance is a material that has a constant composition and has consistent properties throughout the sample. Pure substances can be either elements or compounds.

Carbon dioxide (CO₂) is a pure substance because it is a chemical compound made of one type of molecule consisting of one carbon atom and two oxygen atoms. It has a fixed composition and properties, making it a pure substance.
In contrast:

Soda is a mixture that consists of various substances, including water, sugar, flavorings, and carbon dioxide. Since it is composed of multiple ingredients, it is not a pure substance.

Gasoline is also a mixture, primarily composed of various hydrocarbons and additives. It does not have a fixed composition, making it a mixture rather than a pure substance.

Saltwater is a mixture of salt (sodium chloride) and water. Since it can have varying amounts of salt dissolved in it, it is not a pure substance but a solution (a homogeneous mixture).

Therefore, carbon dioxide is the only pure substance among the options provided.