The intended purpose of the author for the essay where he explains what each type of ads is and provides examples is to inform the reader about the different types of advertising formats. (first option)
Purpose is an author's objective or goal when writing. He may, for example, have the purpose to inform readers of a fact, to persuade them to do something, or to simply keep them entertained.
The question describes an essay where the author lists different types of advertising formats, explains each one of them and provides an example to illustrate them. This type of text has the purpose to inform.
In other words, the author's purpose is just to convey information to readers. He is not trying to convince them of anything nor to keep them entertained.
With the information above in mind, we can choose the first option as the correct answer.
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