Answer:
If two or more atoms of the same element combine, they produce a molecule, for example, H2, O2, O3, etc.
If, however, two (or more) atoms of different elements combine, they produce a compound, for example, NO, CO, FeS, NaCl, etc. The compound may be called a molecule if it is made of independent units, such as NO and CO. However, FeS and NaCl are not molecules because there is no independent unit made of one atom of Fe and a single atom of sulfur or a single unit of Na and Cl. These compound are made of a network of large number of ions of Fe^+2 and S^-2 and Na^+1 and Cl^-1 as a ionic crystallines. If you could isolate a single FeS or NaCl (for example in the gaseous state) you could call them also molecules.
Explanation:
