Rank the compounds in each group in order of increasing strength of intermolecular forces:
a. CH$_3$NH$_2$, CH$_3$CH$_3$, CH$_3$CI
b. CH$_3$Br, Ch$_3$I, CH$_3$Cl
c. (CH$_3)_2$C = C(CH$_3)_2$, (CH$_3)_2$CHCOOH, (CH$_3)_2$CHCOCH$_3$
d. NaCl, CH$_3$OH, CH$_3$Cl