Final answer:
Isopentane yields three isomeric monochlorides upon photochemical chlorination, and neopentane yields four because of the unique hydrogen environments in each molecule.
Step-by-step explanation:
The student's question pertains to the identification of isomeric alkanes with the molecular formula C₅H₁₂ that yield different numbers of monochlorinated isomers upon photochemical chlorination. For an alkane to yield three monochloride isomers, it must have three types of hydrogen atoms that can be replaced to create unique structures.
The isomer of pentane that meets this criterion is isopentane (also known as 2-methylbutane), which has three different types of hydrogen environments: the methyl group on the second carbon, the methyl groups at the ends of the chain, and the methylene hydrogen atoms. On the other hand, an alkane yielding four isomeric monochlorides must have four types of hydrogens. The isomer of pentane that fits this description is neopentane (also known as 2,2-dimethylpropane), featuring a central carbon atom bonded to four methyl groups, each providing a unique environment for chlorination.