(a) What is a homologous series? Explain with an example. (b) State two characteristics of a homologous series. (c) The molecular formula of an organic compound is C18H36. Name its homologous series. (d) Select the hydrocarbons which belong to the same homologous series. Give the name of each series. CH4, C2H2, C2H4, C2H6, C4H10, C3H4, C3H6 (e) What is meant by 'heteroatom'? Give examples. Write the names and formulae of two organic compounds containing different heteroatoms.