Which of the following would be used to seal off the end of a drainage pipe?

The appropriate choice for sealing off the end of a drainage pipe is a cap. A cap is specifically designed to fit over the opening of a pipe, effectively closing it off and preventing any drainage or air from escaping. This is often utilized when a pipe is not in use, or when a system needs to be temporarily sealed for maintenance or alteration purposes.

Using a cap ensures that the integrity of the drainage system is maintained by preventing leaks and potential blockages. In plumbing and drainage systems, sealing off ends of pipes is crucial for maintaining proper function and preventing issues such as backflow or pressure loss.

In contrast, coupling, reducer, and return bend serve different purposes. A coupling connects two pipes together, a reducer changes the diameter of the pipe from a larger size to a smaller size, and a return bend allows for a 180-degree turn in piping. These functions do not relate to sealing off the end of a drainage pipe, which further highlights why a cap is the best choice in this situation.