Question

Which of the following is not a heterogeneous matter?

• A. Rock
• B. Smoke
• C. Cement
• D. Clean air

Answer 1

The correct option is D

Clean air

Explanation for the correct option:

(D) Clean air: Clean air is not a heterogeneous matter. It is classified as a homogeneous matter because:

• Clean air consists of only gaseous components like various gases namely Hydrogen $\left({\mathrm{H}}_2\right)$, Nitrogen $\left({\mathrm{N}}_2\right)$, Oxygen $\left({\mathrm{O}}_2\right)$, water vapours, etc.
• As a result, all the gaseous phase constituents intermix with each other to create uniformity in the composition of air throughout.
• There is no clear boundary of separation in the clean air.

Homogeneous matter: Any substance that exhibits uniformity in its composition and properties throughout its mass is known as a homogeneous matter. Homogeneous matter can be further divided into two parts i.e.;

• Pure substances: When only one type of constituent particles are present in the substance. Example: Substances like Copper $\left(\mathrm{Cu}\right)$, Iron $\left(\mathrm{Fe}\right)$ , etc. and substances like Water$\left({\mathrm{H}}_2\mathrm{O}\right)$, Hydrochloric acid $\left(\mathrm{HCl}\right)$
• Homogeneous mixture: When more than one type of constituent particles are present in a substance. Example: A solution of salt and water, tea, clean air, etc.

Explanation for the incorrect options:

(A) Rock: Rock is an example of heterogeneous matter as it contains various substances like minerals, crystals, etc. and there is no uniformity in its composition and properties throughout.

• Heterogeneous matter: Any substance that does not exhibit uniformity in its composition and properties throughout its mass is known as a heterogeneous matter. Example: Muddy water, Sand, and Iron $\left(\mathrm{Fe}\right)$ nails combined together.

(B) Smoke: Smoke is a heterogeneous matter as smoke is a mixture of gases and Carbon $\left(\mathrm{C}\right)$ particles distributed in between the gases in any proportion.

• It does not have a uniform composition and properties throughout as there is a boundary of separation between particles of carbon and gases present in smoke leading to non-homogeneity.

(C) Cement: It is also a heterogeneous matter as it comprises of various substances like Calcium sulphate $\left({\mathrm{CaSO}}_4\right)$ mixed with Silica $\left({\mathrm{SiO}}_2\right)$, Alumina $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ etc.

Hence, option (D) is correct.