A have no potential energy
4. A
because PbCl2 is an ionic compound and it's solid, so it's a substance.
It cannot be mixture, because it's a pure molecule.
5. D
despite that both substances are gases, colorless they are different molecules, so they should have different either chemical and physical properties
6. C
this substance made from W atoms and others are made from molecules
Other systems in the body might respond with cramps or overheating, which might eventually kill you, if not taken care of in time. Hope this helps!
