Is there a single word that encapsulates the idea of a question and answer pairing or grouping? So far, google has turned up nothing helpful on the topic. Naturally, reviewing the options for both questions and answers in a thesaurus turns up nothing because the alternatives are similar to the idea of one or the other, but not both combined.
Supplementing FF's answer:
Question and answer
Q & A
This might be esoteric and on the edge, but we don't really know the context for OP's query:
What came to mind was a "challenge". When you can't remember your password on your banking site, as an example, they will give you a "challenge", a "challenge question", or a "security question" (I've heard all three). They would seem different from a regular question in that there is supposed to be only one acceptable answer paired to the question portion of the challenge. A soldier on guard duty might also issue a challenge that would need to be returned with the correct paired answer.
Just an idea. "Challenge" was single word as requested. Like I say, we don't have a lot of information.