In a solution, a is the substance being dissolved

In a solution, a SOLUTE is the substance being dissolved.

In a solution, a SOLVENT is the substance in which something is dissolved.

For example in salt water, the salt is the solute. And the water is the solvent. Usually, which substance has a larger amount in the solution can be called a solvent. It doesn't matter if it's a gas, solid, or liquid. They can all be solute or solvents.

B. that is the answer