Which of the following alkanes give only a single monochloro constitutional isomer on reaction with $\mathrm{Cl}{}_2$ and light?

Cyclohexane has twelve equivalent H, and 2,2,3,3-tetramethylbutane has eighteen equivalent H (six methyl groups), so each gives one product. 2,3-Dimethylbutane has primary and tertiary H (2 products) and propane has primary and secondary H (2 products).