Question: Molecules of a solid :
(a) are always in a state of motion
(b) move only when heated
(c) move because they are loosely bound
(d) do not move at all
I could safely ignore (c), as molecules in a solid are tightly bound. My book says that molecules in a solid vibrate about their fixed position. But they also expand on heating. Due to this, I am totally confused whether the correct option (a) or (b) (or maybe (d)?)
I know the question I am asking is really basic, and maybe does not even belong here, but I searched many sites and none revealed satisfying information. And thus, I am looking for expert help. I even doubt if my book (from where this question is) is correct or not.
Thanks a lot.