Two alternatives

A question with only two possible outcomes is called a binary question. Example: "Yes" or "No".

This question type is recommended for advanced decision stages, where deliberation has progressed to a pivotal point. In earlier, more explorative phases, the cognitive benefit of this question type is rather limited, therefore you should consider a different type might produce more differentiated thinking.

PS: Strictly speaking, "two alternatives" is a pleonasm, in the original sense of the word (latin: alter, -a) there is always but one alternative to the status quo.