Final answer:
Iodine (I2) exhibits stronger dispersion forces, and thus stronger attraction, compared to chlorine (Cl2) because it is larger and heavier. As a result, I2 is a solid at room temperature, reflecting these stronger attractive forces.
Step-by-step explanation:
When comparing the attractions between molecules of I2 and Cl2, it is the dispersion forces that we must consider to determine which exhibits stronger intermolecular attractions. Dispersion forces, also known as London dispersion forces, are the result of temporary fluctuations in the distribution of electron density within molecules or atoms. These forces are generally stronger in larger and heavier atoms and molecules because there is a greater electron cloud that can become temporarily distorted, leading to a stronger temporary dipole.
Among the halogens, we observe that iodine (I2) is a solid at room temperature, whereas chlorine (Cl2) is a gas. This indicates that iodine molecules have stronger intermolecular attractions compared to chlorine molecules. This is due to iodine's larger atomic size and mass, resulting in more significant dispersion forces. Therefore, between the pair I2 or Cl2, I2 exhibits stronger attraction due to these forces.