The correct statement about molecules is:
All molecules of a compound have the same properties.
A molecule of a compound is made up of two or more atoms that are chemically bonded together, and all molecules of a particular compound will have the same composition and therefore the same properties.
To clarify the other statements:
- "Each molecule of a compound has different properties" is incorrect; all molecules in a compound have identical properties.
- "All molecules of a compound have one type of atom" is also incorrect; a compound is defined by having two or more different types of atoms.
- "Each atom of a molecule is the same" is incorrect because a compound consists of different types of atoms bonded together.