Name the homologous series to which the hydrocarbon belongs. 2. Draw the structural formula and name the fourth member of the homologous series to which the hydrocarbon belongs.

Here are the answers to your questions:

2. i) Name the homologous series to which the hydrocarbon belongs? The hydrocarbon belongs to the alkane homologous series.

   ii) Draw the structural formula and name the fourth member of the homologous series to which the hydrocarbon belongs?
   The fourth member of the alkane homologous series is butane.
   Its structural formula is:

   $$\begin{matrix} H & H & H & H \\ | & | & | & | \\ H & - & C & - & C & - & C & - & C & - & H \\ & | & & | & & | & & | \\ & H & & H & & H & & H \\ \end{matrix}$$

   Or more simply: $CH_3CH_2CH_2CH_3$

3. Explain why a solution of hydrogen chloride in water turns blue litmus paper red but a solution of hydrogen chloride in methylbenzene has no effect on litmus papers. Hydrogen chloride ($HCl$) is a covalent compound. In water, it ionizes to produce hydrogen ions ($H^+$) and chloride ions ($Cl^-$). The $H^+$ ions are responsible for the acidic properties, causing blue litmus paper to turn red. In methylbenzene (a non-polar solvent), $HCl$ does not ionize. It remains as covalent $HCl$ molecules, and no $H^+$ ions are produced. Therefore, it does not exhibit acidic properties and has no effect on litmus paper.