A mixture is a physical combination of two or more substances that retain their individual chemical properties. A solution is a homogeneous mixture of two or more substances in which the solute is evenly distributed throughout the solvent.

In the case of gravel and water, gravel is a solid and water is a liquid. When these two substances are combined, they form a heterogeneous mixture because gravel does not dissolve in water. The gravel particles will settle at the bottom of the container, and the water will remain on top.

Therefore, gravel and water is a mixture, not a solution.