If your science teacher says B, it’s probably because water has a negative and positive end, heat is just a form of energy, as other atoms can’t leave (they’re attracted to the ends) they are being insulated; but notice that ice will melt into gas (where atoms have tons of space) for other atoms to escape. Hence ice and gas aren’t ideal. (Air is a gas here.) It’s not a 100% but hopefully it helps with some kind of analogy.
The electron cloud is an informal term in chemistry and physics. This region describes the negatively charged electrons in their orbit surrounding the nucleus in an atom. The nucleus has protons in it that have a positive charge on it. It is not easy to know where exactly an electron in any specific time but the electron cloud helps to know electron is moving in this specific area.
