Final answer:
Three constitutional isomers of C9H20 are nonane, 2,2-dimethylhexane, and 3-ethylhexane.
Step-by-step explanation:
Isomers are compounds that have the same molecular formula but different structural formulas. In the case of C9H20, there are three constitutional isomers. The first isomer is called nonane, and its structural formula is CH3(CH2)7CH3. The second isomer is called 2,2-dimethylhexane, and its structural formula is CH3(CH2)3CH(CH3)2. The third isomer is called 3-ethylhexane, and its structural formula is CH3(CH2)3CH2CH2CH3.