Which instrument is primarily used to evacuate fluids during dental procedures?

The saliva ejector is primarily used to evacuate fluids during dental procedures, making it the correct choice. This instrument is designed to remove saliva and other fluids from the patient's mouth, helping to keep the area dry and clear for the dentist to work effectively. It typically consists of a flexible tube that allows for gentle suction, which helps maintain visibility and a clean working environment during various dental treatments.

In contrast, a blade is used for cutting tissues, a file is typically employed in endodontics for cleaning and shaping root canals, and a scalpel is a surgical instrument also used for cutting. These tools serve different purposes and are not specifically designed for fluid evacuation during dental procedures.