Q: How many alternatives should a multiple-choice question have?
Unless you have a specific subject that demands more than five possible alternatives (say, doing a unit on the solar system, having all 8 planets as alternatives might make sense -- though a matching question would probably work better!) don't do it! The more alternatives, the worse your question is likely to be. Four or five alternatives are standard on professionally designed test (since statistically, this reduces the score students could get by pure chance to 25 or 20% respectively). Some people want to pile on alternatives to make the questions 'tougher' and to 'eliminate chance'. But here's the thing -- having 7 alternatives does reduce the chance of them getting the question right by blind guessing, but why bother? Once they've gotten less than 20%, how much more failed do they need to be? And while theoretically reducing the impact of chance on getting the right answer, the more answers the student has to read through, the more it becomes a readiing test rather than a test of that subject matter. So do we really want to eliminate chance factors by penalizing poor readers, ESL students, and so on. Most test designers agree the trade off isn't worth it!
And in the real world, coming up with 7 or 8 credible alternatives becomes REALLY hard. Again, unless there are an obvious 8 possible choices like the 8 planets of the solar system, you will drive yourself crazy trying to come up with credible but clearly wrong answers six, seven and eight. Why do this to yourself?
Or, people will do terrible things like having alternative 5 as "A and B, but not C". No, no no! ? Never do this! It becomes a test of reading and logic rather than subject knowledge. Students will hate you with justification since the test will not be an accurate reflection of what they know -- indeed, some research suggests that this INCREASES the importance of luck...
But here's the killer -- research in the early 1990s suggested that the overall quality of tests DECLINCED with the increase in number of alternatives per question. Everyone who has ever designed an mc test knows that coming up with the answer is easy, the first two wrong answers pretty easy, it's alternative 4 that's tough, and #5 is almost impossible -- the higher you go, the more desperate one becomes to fill the last spot. So, a test with seven alternatives will reduce the writer to grasping at straws, and they will end up accepting ridiculous alternatives that even those completely ignorant about the subject will have no trouble eliminating -- a complete waste of space and student reading. And then -- this is where human nature gets interesting -- since I've given up and accepted a stupid alternative for this question in desperation, my standards for writing the next question go down, because even though I know this is a terrible alternative, it is not as bad as the last one. Or, having accepted three weak ones, what's one more? Pretty soon, the test is garbage.
In contrast, tests with 3 alternatives (the right answer and two wrong alternatives) turn out to be easier to write, and therefore are written to a much higher standard. Students perceive them to be much tougher tests! And, research says, they really are more valid and reliable! So, I tell my students to write questions with three (good!) alternatives rather than going for four or five. Professional test designers can go for four or five because we have the time to come up with high quality 'd's and 'e's, but the realities for classroom instructors is that that is not going to happen.
It's true that with only three alternatives, students can get 33% just by blind luck, but um, so what? I don't know any course where 33% is a pass. Failed is failed. And the results of this test will more accurately reflect what students actually know than one with 7 or 8 alternatives.