Briefly describe the following three methods of speech delivery: scripted speeches, extemporaneous speeches, and impromptu speeches. Give an example of when each method would be most appropriate.

What will be an ideal response?

An impromptu speech is one that is delivered with only seconds or minutes of advance notice for preparation and is usually presented without referring to notes of any kind. This kind of speech would happen in situations such as performance review interviews, or when speaking to the media.
In contrast, a scripted speech is one that is prepared by creating a complete written manuscript and then delivered by reading from or memorizing a written copy. Scripted speeches take a lot of time to prepare, as the delivery should sound conversational and animated even though it is entirely planned. These types of speeches are usually reserved for important occasions with important consequences. For example, political speeches or keynote addresses at conventions are usually scripted speeches.
Most speeches are delivered extemporaneously. An extemporaneous speech is researched and planned ahead of time, but the exact wording is not scripted and will vary somewhat from presentation to presentation. When speaking extemporaneously, you refer to speaking notes reminding you of key ideas, structure, and delivery cues as you speak. They are the easiest to give effectively, and are used in all kinds of settings, such as a classroom presentation, or a public rally.