Final answer:
The liquid such as saline or water used to reduce the concentration of an active agent is known as a solvent. Dilution is the process of adding a solvent to a solution to achieve a desired concentration of the solute.
Step-by-step explanation:
The liquid such as saline or water used to reduce the concentration of an agent is called a solvent. When a solvent is added to a solution to decrease the solute concentration, this process is known as dilution. Dilution is a crucial practice in various fields, including biology, medicine, and chemistry, to prepare solutions of a desired concentration. For instance, commercial pesticides which are typically more concentrated than needed, require dilution before application on crops. This ensures that the active ingredients are at an effective and safe concentration for use.