Isomeric pair that represent a chain, positional and functional group isomerism for CH3CH2CH=CH2

Positional - 2-butene

Functional - cyclobutane

Chain - 2-methylpropene

Explanation:

Isomers are organic molecules having the same molecular formula but different structural arrangements.

Positional isomers have the functional group placed in a different part of the molecule. For example in this particular example, n-butene has the double bond between the 1st and second carbon, counting from the right. Now if we place the double bond between the 2nd and 3rd carbon atom counting from the right, we have something of this nature:

CH3CH=CHCH3

We have simply shifted the double bond. This new compound is called 2-butene and it is a positional isomer of n-butene

Functional group isomers looks at organic molecules in different homologous series that have the same molecular formula as n-butene. Without going too far, we can see that the cycloalkanes bear resemblance to the alkenes in this case. They both share the molecular formula CnH2n.

Hence, cyclobutane is a functional group isomer of n-butene

Lastly, a chain isomer just shows a different arrangement of the carbon skeleton. For this particular example, we can see that 2-methylpropene shows a skeleton rearrangement of the n-butene molecule