Final answer:
The hydrocarbon C₅H₁₀ that forms a single monochloro compound C₅H₉Cl when reacted with chlorine in sunlight is 2-methylbutane, a symmetrically branched alkane.
Step-by-step explanation:
The hydrocarbon C₅H₁₀ that does not react with chlorine in the dark but gives a single monochloro compound C₅H₉Cl in bright sunlight is likely to be an alkane. This is because alkanes are saturated hydrocarbons with single bonds between carbon atoms and can undergo substitution reactions with halogens in the presence of light, a reaction known as halogenation.
The formation of only one monochloro compound suggests that the hydrocarbon has identical carbon atoms such that substitution at any of these carbon atoms would yield the same product. Considering the molecular formula C₅H₁₀, the hydrocarbon is most likely 2-methylbutane, which is a branched chain alkane. When substituted with chlorine under sunlight, it forms only one monochloro compound C₅H₉Cl, regardless of which hydrogen is replaced by chlorine, due to the symmetrical nature of the molecule.