Final answer:
The correct answer to the question is 4) A generator, which induces an emf by rotating a coil in a magnetic field.
Step-by-step explanation:
A coil of wire attached to a receiving mechanism and suspended within a magnetic field is a description that can refer to various devices that work on the principles of electromagnetism. However, considering that it's suspended and seems to be part of a system that generates motion or electromotive force (emf), the description best fits an electric generator. Electric generators use the motion of coils within a magnetic field to induce an emf, essentially converting mechanical energy into electrical energy. This process is similar to the operation of electric motors but works in reverse. While electric motors convert electrical energy into mechanical energy, generators work to produce current by rotating coils in a magnetic field.
Transformers, on the other hand, are devices that alter the voltage of alternating current (AC) electricity, and an electromagnet is simply a type of magnet in which the magnetic field is produced by an electric current.
In summary, 4) A generator is the correct answer to the question.