Which of the following correctly describes a solution?

A solution is defined as a homogeneous mixture where a substance (the solute) is fully dissolved in another substance (the solvent), typically a liquid. In this case, the correct choice describes a situation where a solute is dissolved in a liquid, resulting in a consistent and uniform composition throughout the mixture.

When a substance dissolves, it breaks down into its individual particles, which become evenly distributed and cannot be easily separated by physical means, such as filtration. This characteristic distinguishes solutions from other types of mixtures, where components may retain their physical properties and can often be separated mechanically.

In comparison, the other options reflect characteristics of different types of mixtures, such as suspensions or colloids, where separation methods such as filtration may be applicable or where solid particles do not fully dissolve, resulting in a heterogeneous mixture. Thus, the definition of a solution is best captured by the description provided in the correct answer, emphasizing its homogeneous nature and the dissolution process.