Which one of the following has the lowest boiling point? A C H 3 ​ C l B C 2 ​ H 5 ​ C l C C 2 ​ H 5 ​ B r D C 2 ​ H 5 ​ I

							Figuring out the order of boiling points is all about understanding trends. The key thing to consider here is that, boiling points reflect the strength of forces between molecules. As the molar mass increases the boiling point increases.
There are 3 important trends to consider:
The relative strength of the four intermolecular forces is: ionic > hydrogen bonding > dipole dipole > van der Waal's dispersion forces.The influence of each of these attractive forces will depend on the functional groups present.
Boiling point increase as the number of carbons is increased. Branching decreases boiling point.
						

							
ANSWER
Figuring out the order of boiling points is all about understanding trends. The key thing to consider here is that, boiling points reflect the strength of forces between molecules. As the molar mass increases the boiling point increases.
There are 3 important trends to consider:
The relative strength of the four intermolecular forces is: ionic > hydrogen bonding > dipole dipole > van der Waal's dispersion forces. The influence of each of these attractive forces will depend on the functional groups present. 
Boiling point increase as the number of carbons is increased. Branching decreases boiling point.