Which research question would be most appropriate for a four- to five-page research paper? Does anyone know??

The first question isn't a research paper, or if it were, it would be much longer than four to five pages. A "major emotional reaction" is either going to be subjective or is going to require a significant amount of research and explanation to explain, both of which are prohibitive in this case.

The second question is also broad for such a small research paper. You would be hard-pressed to get through even addressing what effectively addressing bullying even means, much less to assess whether or not elementary schools are presently doing so.

The fourth question, on the other hand, is a bit narrow. It could be answered in a single sentence.

That leaves the third question. While broad, it's neither vague nor does it contain elements that would prevent you from succinctly answering the question in the given space, i.e., providing the reasons bullying exists within four to five pages.

Well, first you're going to have to define "bullying," which has become a rather meaningless word. It seems to include everything from committing murder all the way down to sticking your tongue out at someone.