For a substance of composition c7h16, write down any three isomers.

С7Н16 is an alkane, therefore all bonds are saturated, its structural formula looks like:
CH3-CH2-CH2-CH2-CH2-CH2-CH3 – heptane.
Isomers are substances that have the same qualitative and quantitative composition, but different structures. In this case, it is 7 carbon atoms and 16 hydrogen atoms.
CH3-CH2-CH2-CH2-CH (CH3) -CH3 – 2-methylhexane;
CH3-CH2-CH2-C (CH3) 2-CH3-2,2-dimethylpentane;
CH3-CH2-CH (CH3) -CH (CH3) -CH3 – 2,3-dimethylpentane;
CH3-CH2-CH2-CH (CH3) -CH2-CH3 – 3-methylhexane.