What is meant by isomerism ? Why do first three members of the alkane series not show isomerism ? Write the structure of two isomers of the fourth member of this series.

Explanation

Isomerism is the existence of two or more compounds having same molecular formula but different structures.
It is not possible for them to have different structures/only one structure is possible for each of them.
Structures: `CH_(3)-CH_(2)-CH_(2)-CH_(3)," "CH_(3)-underset(CH_(3))underset(|)"CH"-CH_(3)`