What is meant by isomers? Draw the structures of two isomers of butane, C4H10

What is meant by isomers? Draw the structures of two isomers of butane, C4H10. Explain why we cannot have isomers of first three members of alkane series.

Answer:

Isomers are compounds having the same molecular formula but different structures.
The two isomers of butane, C4HI0 are:
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Since branching is not possible, isomers are not possible for the first three members of alkane series.