Homogeneous and heterogeneous mixtures

Correct answer: A. Air is a homogeneous solution of gases; smoke is dispersion of solid particles in gas

Clean air is treated as a homogeneous mixture of gases, with gases uniformly distributed. Smoke contains tiny solid particles, such as soot, dispersed through a gas; it is therefore a dispersion rather than an ordinary gas-gas true solution. Smoke is not necessarily pure and does not contain only liquid particles.

Correct answer: A. Because a solid solution must also be homogeneous

A solid solution is still a solution, so it must have a sufficiently uniform composition throughout the solid phase. If the alloy components are unevenly distributed, different regions have different compositions and the material behaves as a heterogeneous mixture or multiphase material. Alloys can contain solid solutes, and metals are not gases, so the other explanations are false.