Final answer:
The pair of molecules that is expected to have the most different properties is H₂O and H₂S, due to their different chemical compositions and structures.
Step-by-step explanation:
The pair of molecules that is expected to have the most different properties is (c) H₂O and H₂S. Water (H₂O) and hydrogen sulfide (H₂S) have different chemical compositions and structures, resulting in different physical and chemical properties.
Water is a polar molecule, while hydrogen sulfide is a polar molecule.
Water has a higher boiling point and higher surface tension compared to hydrogen sulfide due to stronger intermolecular forces in water.