The alkane that gives only one monochloro product on chlorination with ${\text{Cl}}_2$ in presence of diffused sunlight is:

A hydrocarbon gives only one monochloro product if all its hydrogen atoms are equivalent.In Neopentane (2,2-Dimethylpropane), all 12 hydrogens are present on four identical methyl groups attached to a central quaternary carbon. Thus, replacing any one of them yields the same product (1-chloro-2,2-dimethylpropane).