F.5 Chem about boiling point

just a guess.
the overall polarity of molecules is very similar: an alkyl plus a chlorine.

boiling point depends on intermolecular attraction.
in this case, there's permanent dipole attraction.

the dipole moment is greater with longer molecule, the concept is similar to induced dipole.
1-chloropropane is longer than 2-chloropropane in terms of length. thus the resulted dipole attraction is a little bit stronger.

however, the difference in b.p. is very small, so the effect may not be that pronounced...