One of my kids had the same sort of quiz/test given, but he and his friend had a concern with it. When I read it, I was inclined to agree with them that it doesn't work the way the writer intends.
Presumably, each question contains an instruction to follow. Being instructed to read all questions first doesn't mean you then do what any of the other questions instruct. Why, after reading all other 99 questions first, do you do what question 100 instructs but not what the others instruct?
Because you get in the mind of the test-giver and correctly predict the point they're trying to make and act accordingly. If you can't or won't, you fail. That's what school is about, after all.
Sadly true, which leads to a conundrum when trying to get inside the test-giver's head: did the test-giver notice this intricacy of the question and therefore I should give the clever answer, or did they not realise and therefore I should give the naive answer?
In this particular instance, my son and his friend were unable to convince their teacher that the test/quiz was flawed, so the naive answer was the "right" one to win the teacher's approval.
Presumably, each question contains an instruction to follow. Being instructed to read all questions first doesn't mean you then do what any of the other questions instruct. Why, after reading all other 99 questions first, do you do what question 100 instructs but not what the others instruct?