[Solution by Claude - not from source] The compound is 2-methylbutane. Monochlorination gives: 1-chloro-2-methylbutane (chiral, 2 stereoisomers), 2-chloro-2-methylbutane (1), 2-chloro-3-methylbutane (chiral, 2), and 1-chloro-3-methylbutane (1). Total $=6$. Answer (4).