Which of the following is an example of a solution?

• A. Sand
• B. Oil and water
• C. Salt water
• D. Granite

Answer: (C)

A solution is a homogeneous mixture in which a substance dissolves in another, giving a uniform composition throughout. Salt dissolves in water, so salt water is formed when the solute (salt) disperses evenly in the solvent (water). The ions and molecules mix at the molecular level, so you can’t see the salt and there’s no separate layer or distinct particles. That uniform, single-phase nature is what defines a true solution.

Sand isn’t a solution because it’s a mixture of solid grains; you can see and physically separate the different particles, so it remains heterogeneous. Oil and water don’t form a solution either—they don’t mix and stay in separate layers due to immiscibility. Granite is a solid rock composed of minerals bound together, not a dissolved substance in a solvent.

So the example that fits a solution is the one where salt is dissolved in water, creating a uniform salt water solution.