Which statement best defines a colloid?

Which statement best defines a colloid?

• A. A suspension of particles in a dispersion medium such as water.
• B. A pure substance with a fixed composition.
• C. A solution with uniform composition.
• D. A gas dissolved in a liquid.

Answer: (A)

A colloid is a mixture in which very small particles are dispersed throughout a medium. The key idea is that there are tiny particles spread evenly in another substance, forming a system where the dispersed phase does not dissolve completely and tends to stay suspended rather than settling out quickly. Saying it as a suspension of particles in a dispersion medium like water captures this setup: the particles are dispersed in the water rather than forming a single uniform substance. This differs from a pure substance with fixed composition (which would be a single, unchanging material), or a true solution with uniform composition (where substances are dissolved at the molecular level), or a gas dissolved in a liquid (which is also a solution). Colloids include familiar examples like milk, fog, and gelatin.

A colloid is a mixture in which very small particles are dispersed throughout a medium. The key idea is that there are tiny particles spread evenly in another substance, forming a system where the dispersed phase does not dissolve completely and tends to stay suspended rather than settling out quickly. Saying it as a suspension of particles in a dispersion medium like water captures this setup: the particles are dispersed in the water rather than forming a single uniform substance. This differs from a pure substance with fixed composition (which would be a single, unchanging material), or a true solution with uniform composition (where substances are dissolved at the molecular level), or a gas dissolved in a liquid (which is also a solution). Colloids include familiar examples like milk, fog, and gelatin.