The octane number $100$ is assigned to .............

An alkyl bromide $(X)$ reacts with $Na$ in the presence of dry ether to form $4, 5-$diethyloctane. Compound $(X)$ is

In which of the following reactions does the carbon number not change on product formation?
$(i)$ Hydrogenation
$(ii)$ Alkyl halide reduction
$(iii)$ Wurtz reaction
$(iv)$ Decarboxylation
$(v)$ Kolbe reaction

$A$ hydrocarbon $C_5H_{12}$ does not react with chlorine in the dark but gives six monochloro compounds in bright sunlight. The hydrocarbon is:

Which of the following has the minimum boiling point?

$n$-pentane and isopentane can be distinguished by