Which branched-chain isomer of the hydrocarbon with molecular mass 72 u gives only one isomer of mono-substituted alkyl halide?

Neopentane, when reacted with Cl2 and undergoes monohalogenation, gives a single product. This is because all the hydrogen atoms in neopentane are equivalent. Replacing any one of them with a chlorine atom results in the same 2-chloro-2-methylpropane (also known as tert-pentyl chloride).