The correct option is C 1, 2 and 4 belong to the same homologous series
A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series. 1, 2 and 4 have same functional group (-COOH), so they are homologous in nature. The functional group of propanone is ketone, so it is not homologous with 1, 2 and 4. Again C2H6 does not have any functional group, so it is not homologous with 1, 2 and 4.