Draw formulas for the first five members of each homologous series beginning with the following compounds.
$(a)$ $HCOOH$ $(b)$ $CH_{3}COCH_{3}$ $(c)$ $CH_{2}=CH_{2}$

The first five members of each homologous series are generated by adding successive $-CH_{2}-$ units:
$(a)$ $HCOOH$ (Methanoic acid),$CH_{3}COOH$ (Ethanoic acid),$CH_{3}CH_{2}COOH$ (Propanoic acid),$CH_{3}CH_{2}CH_{2}COOH$ (Butanoic acid),$CH_{3}CH_{2}CH_{2}CH_{2}COOH$ (Pentanoic acid).
$(b)$ $CH_{3}COCH_{3}$ (Propanone),$CH_{3}COCH_{2}CH_{3}$ (Butanone),$CH_{3}COCH_{2}CH_{2}CH_{3}$ (Pentan$-2-$one),$CH_{3}COCH_{2}CH_{2}CH_{2}CH_{3}$ (Hexan$-2-$one),$CH_{3}COCH_{2}CH_{2}CH_{2}CH_{2}CH_{3}$ (Heptan$-2-$one).
$(c)$ $CH_{2}=CH_{2}$ (Ethene),$CH_{3}CH=CH_{2}$ (Propene),$CH_{3}CH_{2}CH=CH_{2}$ (But$-1-$ene),$CH_{3}CH_{2}CH_{2}CH=CH_{2}$ (Pent$-1-$ene),$CH_{3}CH_{2}CH_{2}CH_{2}CH=CH_{2}$ (Hex$-1-$ene).