The normal boiling point of CCl₄ is 77ºC, whereas that of CBr₄ is 190ºC. Why does CBr₄ have a higher boiling point than CCl₄?

A. CBr₄ molecules are smaller and less massive.
B. CBr₄ molecules have stronger London dispersion forces.
C. CCl₄ molecules have stronger hydrogen bonding.
D. CBr₄ molecules have lower vapor pressure.

CCl4 has a lower boiling point than CBr4 because CBr4 molecules have stronger London dispersion forces due to the larger electron cloud and mass of bromine atoms, which require more energy to overcome.

Explanation:

The higher boiling point of CBr4 compared to CCl4 is due to the strength of intermolecular forces present in the substances. Considering the given options, the correct reason is that CBr4 molecules have stronger London dispersion forces compared to CCl4. This is because CBr4 is more massive than CCl4, containing heavier bromine atoms, which leads to a larger electron cloud and more polarizable molecules. Consequently, the increased London dispersion forces require more energy to overcome, resulting in a higher boiling point for CBr4.

Options regarding smaller size (option 1), hydrogen bonding in CCl4 (option 3), or lower vapor pressure in CBr4 (option 4) do not apply since neither CCl4 nor CBr4 can form hydrogen bonds, and vapor pressure is a consequence rather than a cause of boiling point differences.