By how many $-{\mathrm{CH}}_2-$ (methylene) units do the formulae of the first two members of homologous series of alkanes, methane $\left({\mathrm{CH}}_4\right)$ and ethane $\left({\mathrm{C}}_2{\mathrm{H}}_6\right)$ differ? Similarly, by how many $-{\mathrm{CH}}_2-$ units do the neighbouring members ethane $\left({\mathrm{C}}_2{\mathrm{H}}_6\right)$ and propane $\left({\mathrm{C}}_3{\mathrm{H}}_8\right)$ differ from each other?

The table given below shows the homologous series of alkenes. Inspect the molecular formulae of the members of this series. Do you find any relationship, in the number of carbon atoms and the number of hydrogen atoms in the molecular formulae?

What would be the general formula for the molecular formulae of the members of the homologous series of alkanes? What would be the value of ‘n’ for the first member of this series?

The general molecular formula for the homologous series of alkynes is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}-2}$. Write down the individual molecular formulae of the first, second and third members by substituting the values 2,3 and 4 respectively for ‘n’ in this formula.