Question

How does a solution differ from a colloid?

Answer 1

Colloids contain two distinct phases separated by an interface. Solutions contain one distinct phase, and no interface.

Explanation:

Take a typical colloid, e.g. pigmented ink.
The tiny particles of pigment are uniformly distributed throughout the carrier liquid, but if you look at it under a microscope you can see the many tiny little particles of pigment, with a clear interface between the pigment and the liquid (it is the surface of the little particles).

Now take a solution, like salt water. Look at this under a microcope and you see....nothing. The reason is that solutions are single phase, where the solute is effectively broken up into component ions and solvated by the solvent molecules. No physical "interface" exists.