Introduction:
Solubility is a property that describes the ability of a substance to dissolve in another substance to form a homogeneous solution. In this case, the substance that dissolves is called the solute, and the substance in which the solute dissolves is called the solvent.

Explanation:
To answer this question, we need to understand the definitions of solute and solvent, as well as how they relate to the process of solubility.

Solute:
A solute is a substance that is being dissolved in a solution. It can exist in various states, such as solid, liquid, or gas. When a solute is added to a solvent, it may undergo a physical or chemical change to form a homogeneous solution.

Solvent:
A solvent is a substance that is capable of dissolving other substances. It is usually a liquid, but it can also be a solid or gas. The solvent is responsible for dissolving the solute particles and forming a homogeneous solution.

Example:
Let's take an example to illustrate this concept. If we have a solid substance like sugar (solute) and we add it to water (solvent), the sugar particles will dissolve in the water to form a sugar-water solution. Here, sugar is the solute, and water is the solvent.

Solution:
When a solute is dissolved in a solvent, it forms a homogeneous solution. A homogeneous solution is a mixture where all the components are evenly distributed at a molecular level. This means that the solute particles are dispersed uniformly throughout the solvent, resulting in a uniform composition and appearance.

Conclusion:
In conclusion, solubility is the property of a substance (solute) to dissolve in another substance (solvent) to form a homogeneous solution. The solute can be in any state (solid, liquid, or gas), and the solvent can also be in any state. However, in the context of the given question, the solute is the substance that dissolves, and the solvent is the substance in which the solute dissolves. Therefore, the correct answer is option 'A' - solute, solvent.