The incorrect statement among the following is:

1. A molecule of a compound has atoms of different elements.
2. A compound can not be separated into its constituent elements by the physical method of separation.
3. A compound retains the physical properties of its constituent elements.
4. The ratio of atoms of different elements in a compound is fixed.
Hint: Compound contains two or more than two elements combined together in a fixed proportion by mass .
A compound is a pure substance containing two or more than two elements combined together in a fixed proportion by mass
and which can be decomposed into its constituent elements by suitable chemical methods.
Further, the properties of a compound are quite different from the properties of constituent elements.
e.g., water is a compound containing hydrogen and oxygen combined together in a fixed proportion. But the properties
of water are completely different from its constituents, hydrogen and oxygen.