CBSE Class 10 Science 2017 · Paper 31/2/C · Question 11

A homologous series is a series of carbon compounds that have the same functional group substituting for hydrogen in a carbon chain, and therefore similar chemical properties; any two successive members differ by a $-{\text{CH}}_2-$ unit ($14$ u in molecular mass), and all the members can be represented by one general formula. Fourth member ($n=4$): ${\text{C}}_4{\text{H}}_9\text{OH}$ (butanol). Fifth member ($n=5$): ${\text{C}}_5{\text{H}}_{11}\text{OH}$ (pentanol). Two differences in physical properties between consecutive members: (1) the higher member has a higher boiling point (melting points also rise with molecular mass in general); (2) their solubility in a particular solvent differs - for example, the solubility of the alcohols in water decreases as the chain gets longer.