Final answer:
The sample of air containing various gases including nitrogen and oxygen is accurately described as a homogeneous mixture, because it has a uniform composition throughout and consists of multiple substances combined physically.
Step-by-step explanation:
The sample of air you have described, containing 70% nitrogen (N), 20% oxygen (O), 0.97% argon (Ar), and smaller percentages of other gases such as carbon dioxide (CO2), neon (Ne), helium (He), and methane (CH4), can be described with several terms:
A. Homogeneous: This term applies because the air sample is uniform in composition and appearance throughout, meaning you cannot differentiate between its components with the eye.
B. Heterogeneous: This term does not apply to the air sample. 'Heterogeneous' would suggest that the sample has visibly different parts or phases, which is not the case with air.
C. Mixture: Air is indeed a mixture, as it is composed of two or more substances (gases) that are physically combined but not chemically.
D. Pure substance: This term does not apply. A pure substance would be made of only one type of particle, while air consists of several types of gas molecules.
E. Colloid: This term also does not apply to the sample. A colloid is a mixture where one substance of microscopically dispersed insoluble particles is suspended throughout another substance. Air is not a colloid but rather a gas-gas solution.
Therefore, the sample of air can be accurately described as both homogeneous and a mixture.