Final answer:
Nonpolar compounds like Substance A have weaker intermolecular forces than polar compounds such as Substance B, which is why they have lower melting points. This is because nonpolar molecules exhibit London dispersion forces, which are weaker than the dipole-dipole interactions and hydrogen bonds found in polar molecules.
Step-by-step explanation:
The question asks why Substance A, assumed to be a nonpolar covalent compound, has a lower melting point compared to Substance B, which is identified as a polar compound like hydrogen sulfide. The correct answer to this question is that nonpolar compounds like Substance A have weaker intermolecular forces (IMFs) than polar compounds such as Substance B. Specifically, in most cases, nonpolar molecules exhibit London dispersion forces which are weaker than the dipole-dipole interactions, and especially weaker than the hydrogen bonds commonly found in polar compounds. These intermolecular forces, not to be confused with intramolecular forces which are the covalent bonds within a molecule, are critical in determining the melting and boiling points of substances. The weaker the forces, the lower the temperature at which the molecules can move freely from each other, which means lower melting and boiling points.
Therefore, the correct answer from the options provided is: c) Nonpolar compounds like Substance A have weaker IMEs (intermolecular forces) than polar compounds such as Substance B.