Which of the following veterinary tools is used to administer fluids into an animal?

The IV tube is specifically designed for the administration of fluids directly into an animal's bloodstream through an intravenous route. This tool is crucial in various veterinary settings, especially for hydration, medication delivery, or during surgeries when an animal cannot drink or eat normally. The flexibility and design of the IV tube allow it to connect to an intravenous catheter that is inserted into a vein, making it a safe and efficient method for fluid administration.

In contrast, the scalpel is a surgical instrument used for making incisions and performing surgical procedures, while forceps are used for grasping, holding, or manipulating tissues during surgery or examinations. The drench gun is utilized mainly for administering oral medications or fluids, often in livestock, but it does not administer fluids intravenously. Therefore, the IV tube is the most appropriate tool for the task of administering fluids directly into an animal's circulatory system.