$C_{3}H_{6}$,$C_{4}H_{8}$,and $C_{5}H_{10}$ belong to the same homologous series.
$(i)$ Define homologous series.
$(ii)$ Why are the melting and boiling points of $C_{5}H_{10}$ higher than $C_{4}H_{8}$?
$(iii)$ Arrange these hydrocarbons in order of increasing boiling points.

(N/A) $(i)$ $A$ homologous series is a group of organic compounds having the same functional group and similar chemical properties,in which all successive members differ by a $-CH_{2}$ unit.
$(ii)$ The melting and boiling points of $C_{5}H_{10}$ are higher than those of $C_{4}H_{8}$ because the molecular mass of $C_{5}H_{10}$ is greater than that of $C_{4}H_{8}$. As molecular mass increases,the intermolecular forces of attraction increase,requiring more energy to overcome them.
$(iii)$ The order of increasing boiling points is: $C_{3}H_{6} < C_{4}H_{8} < C_{5}H_{10}$.