That is literally how the school system works in Denmark, too. I’m not sure why he’s taking for granted that anyone would have taken college level chemistry classes. We can pretty much pick and choose what classes we want to take starting around age 16, and once you get to a college level, your classes are just related to whatever degree you’re getting.
The absence of a cat implies nothing is there. So the opposite of a cat is nothing (specifically nothing where a cat should have been).
So, another acceptable answer would be “what is up? Nothing.”