WAEC Chemistry 2017 Paper

Concept:Members of a homologous series have the same functional group and can be represented by a common general formula.Explanation:In a homologous series, successive members differ by a fixed unit of $CH_2$.For example, methane is $CH_4$, ethane is $C_2H_6$, and propane is $C_3H_8$.The difference between each successive pair is $CH_2$.The chemical properties of all members are similar, not gradually changing.Physical properties, such as boiling point, usually change gradually along the series.Members do not have the same molecular formula; each member has a different formula.Therefore, the distinguishing feature is that successive members change by $CH_2$.Answer:D. Successive members undergo changes in molecular formula by $CH_2$.