Which of the following is a solute?

A solute is a substance that is dissolved in a solvent to form a solution. In the context of the choices provided, sugar in a mixture of sugar and water acts as the solute because it is the substance that is being dissolved in the water, which is the solvent.

When sugar is added to water, it breaks down into smaller particles and disperses throughout the water, creating a homogeneous solution. This process demonstrates the characteristic behavior of a solute within a solution. The other options contain substances that either serve as solvents or are not dissolved in a manner that fits the solute definition. For example, in the context of a sugar solution, while water acts as the solvent, sugar operates as the solute, which aligns with the definition and functionality of these components in a mixture.