Answer:
D. Element.
Explanation:
Atoms form elements. Elements form molecules. Molecules form compounds.
Hydrogen molecules are made up of only one element (hydrogen).
Water molecules, H₂O, are compounds because they are made up of more than one element, hydrogen and oxygen.
Some physical properties change, but the substance keeps its identity.
When dealing with these kind of questions, understand that the keyword here is physical change. Thus, all options that says no physical properties change are WRONG. So this leaves us with only 2 answers left. However, this is a physical change, no chemical change. Thus, the substance will keep its identity and not change.