Question

what happens to particles when they are heated? they stop moving; they slow down and compress; they speed up and spread out; they move closer together and speed up

Explanation:

When particles are heated, they gain energy. This increased energy causes them to move (vibrate, translate, rotate) faster (speed up). As they move faster, the intermolecular forces holding them relatively close are overcome more easily, so the particles move further apart from each other (spread out). The other options are incorrect: particles don't stop moving (absolute zero is theoretical and not reached here), heating doesn't make them slow down and compress (cooling would do that), and they don't move closer together (that's what happens with cooling or pressure increase in some cases, not heating).

Answer:

C. They speed up and spread out