You work as a volunteer at the local science museum. You are asked to design an exhibit that
compares the size of a lithium atom to the size of
its nucleus. A lithium atom has a diameter of about
3 X 102 picometers. The nucleus of a lithium atom
has a diameter of about 5 X 10-3 picometers.
There are a trillion (10^12) picometers in a meter.

State the problem in your own words. What decisions will you need to make before you can proceed?

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.