Question

What are isomers isomers of the first three members of alkane series are not possible give reasons to justify?

Answer 1

Isomers are the different structures of the compound having the same (identical) Molecular formula.

Isomers of the first three members of the alkanes are not possible because maximum the third member of the alkane group contains three carbon atoms.
So that carbon atoms cannot be rearranged in any other neo form. Thus it's isomers are not possible.