Solution

Among $$\underset{isonexane}{CH_3 - \overset{CH_3}{\overset{|}{C}H} - CH_2 - CH_2 - CH_3}$$ and $$\underset{3-methyl-pentane}{CH_3 - CH_2- \overset{CH_3}{\overset{|}{C}H} - CH_2 - CH_3}$$ $$CH_3-CH_2-\!\!\underset{\!\! \! H}{\underset{|}{\overset{\,\,\, CH_3}{\overset{|}{C}}}\!\! -} CH_2 - CH_3$$ has higher Boiling point due to symmetry. $$\therefore$$ Boiling point of isohexane is $$60^o$$ To separate two compounds having marginal difference in their boiling point, fractional distillation method is used. In this method, the compound having a low boiling point gets distilled out first. $$\therefore $$ Isohexane will distil out first. $$\therefore$$ method is fractional distillation Hence, the correct option is $$\text{C}$$