At which point(s) will acceleration occur shown in the image???

Gravity is an ever present force, and therefore acceleration is guaranteed to happen at every single one of those points (and in fact, everywhere in the universe).

On top of that, friction will be present in all four spots (friction with the rails, with the air, with the axles, etc.), and friction is a perfectly acceptable force that will cause acceleration, slowing the roller coaster down.

So the correct answer is every single point, regardless of what answer the teacher expects.

d) physical means can be used to separate the components of air.