If it is just a physical change then we can instantly cross out B. and A. as they say in there that they become a new substance and that is not just a physical change. C. is not correct because they combine and there for make a new substance. That leaves D. which makes sense because a physical change would be a change in its size or something that doesn't change the material, this is like when you break a rock, it is now in pieces and smaller but it is still the same rock therefor it is a physical change.
