Chemistry

The key here is recognizing that $C_5H_{10}$ has one degree of unsaturation, which can be satisfied by either a ring or a double bond. For cyclic isomers specifically, you need to draw all possible five-membered ring skeletons, then systematically place the remaining two hydrogens (as a methyl substituent) at each distinct position. The crucial insight is that stereoisomers count separately—cyclopentane with a methyl group can exist as cis and trans isomers depending on where that methyl branch sits relative to other substituents or ring geometry. Map out the ring structures carefully and check which positions are truly different by symmetry.

The key here is recognizing that $C_5H_{10}$ has one degree of unsaturation, which can be satisfied by either a ring or a double bond. For cyclic isomers specifically, you need to draw all possible five-membered ring skeletons, then systematically place the remaining two hydrogens (as a methyl substituent) at each distinct position. The crucial insight is that stereoisomers count separately—cyclopentane with a methyl group can exist as cis and trans isomers depending on where that methyl branch sits relative to other substituents or ring geometry. Map out the ring structures carefully and check which positions are truly different by symmetry.