Colloids

Fog consists of very small liquid water droplets suspended or dispersed through air. Air is a mixture of gases, so the continuous or dispersing medium is gaseous. Therefore, fog represents liquid droplets in a gas. It is not a liquid-in-liquid or solid-in-gas example, because the dispersed particles here are water droplets.

Smoke is made of very fine solid particles, such as soot, carried and dispersed in air. Since the dispersed particles are solid and air is gaseous, smoke is described as a solid-in-gas dispersion. It is not gas in solid or liquid in liquid. Smoke is commonly discussed as an aerosol or colloidal dispersion rather than a true solution.

Smoke contains very small solid particles, such as soot, dispersed through air. These particles remain as a dispersed phase rather than dissolving at the molecular level, so smoke is treated as an aerosol or colloidal dispersion, not an ordinary true solution. It is not a pure gas, a liquid–liquid solution, or particle-free. Therefore, option A is correct.

Fog consists of tiny liquid water droplets dispersed through the surrounding air. Because the droplets remain distinct particles instead of becoming molecularly dissolved, fog is a liquid-in-gas colloidal dispersion rather than a true solution. It is not a solid-in-solid mixture, salt water, or merely invisible water vapour. Hence option A gives the correct description.

In a true solution, solute particles are extremely small and dispersed at the molecular or ionic level, giving a uniform mixture. Colloids contain larger dispersed particles and may show effects such as light scattering, although they can appear uniform to the eye. Solutions do not always show particles or form sediment, and colloids are mixtures, not pure substances.