Final answer:
Chemicals used to dilute illicit drugs are called diluents or cutting agents, and they increase the quantity of the drug while reducing its potency.
Step-by-step explanation:
In the context of illicit drugs, chemicals that are used to dilute the drug and give it more volume are called diluents or cutting agents. Diluents can include various substances such as baking soda, talcum powder, or caffeine. These substances are added to increase the quantity of the drug and make it less potent.