Intermolecular Forces

The melting point of a compound is influenced by the strength of the intermolecular forces between molecules. The presence of chlorine atoms on the benzene ring increases the dipole-dipole interactions and London dispersion forces between molecules. As the number of chlorine atoms increases, the compound's ability to form stronger intermolecular interactions increases, which generally leads to a higher melting point.
The compound with three chlorine atoms attached to the benzene ring will have the highest melting point due to the increased molecular interactions.
Therefore, the correct answer is: