(a) : HCOOH The given compound is formic acid (a carboxylic acid) and the first five members of the carboxylic acid series are : (1) HCOOH (2) $CH_3COOH$ (3) $CH_3CH_2COOH$ (4) $CH_3CH_2CH_2COOH$ (5) $CH_3CH_2CH_2CH_2COOH$ (b) : $CH_3COCH_3$ The given compound, propanone, is a ketone and the first five members of the ketone series are : (1) $CH_3COCH_3$ (2) $CH_3CH_2COCH_3$ (3) $CH_3CH_2CH_2COCH_3$ (4) $CH_3CH_2CH_2CH_2COCH_3$ (5) $CH_3CH_2CH_2CH_2CH_2COCH_3$ (c) : $CH_2= CH_2$ Ethene is an alkene and the first five members of the alkene series are : (1) $CH_2 =CH_2$ (2) $CH_3–CH =CH_2$ (3) $CH_3CH_2 —CH =CH_2$ (4) $CH_3CH_2CH_2—CH =CH_2$ (5) $CH_3CH_2CH_2CH_2-CH= CH_2$