Question

Pentanal and $2 -$Methyl butanal are
A.Chain isomer
B.Positional isomer
C.Functional isomer
D.None of these

Answer 1

Isomers: They are defined as the compounds which are having the same molecular formula but have different molecular structures. Their position may vary with respect to the functional groups, carbon in the longest carbon chain, etc.

Complete step-by-step answer: First of all let us talk about what isomers and their types.
Isomers: They are defined as the compounds which are having the same molecular formula but have different molecular structures. There are two types of isomers
1. structural isomerism
2.Stereoisomerism
Here in this question we will only talk about structural isomerism.
Structural isomerism are further classified into various categories
A.Chain isomerism: In this isomerism the compounds vary with respect to the number of carbon in its longest carbon chain i.e. parent chain.
B.Position isomerism: In this isomerism the compounds vary with respect to the position of the functional group present in the molecule.
C.Functional isomerism: In this isomerism the compound varies with respect to the functional group present in the molecule.
Here we are given with the molecules pentanal and $2 -$Methyl butanal.
Pentanal is $C{H_3}C{H_2}C{H_2}C{H_2}CHO$ and $2 -$Methyl butanal is $C{H_3}C{H_2}CH(C{H_3})CHO$. Here we can see that the functional group in both the molecules is the same i.e. aldehyde and the position of the functional group is same i.e. one but the only difference is the carbon in the longest carbon chain. So it is an example of Chain isomerism. Hence option a is correct.

Note: Stereo isomerism is also of two types
1.Geometrical isomerism: Generally shown by double linked carbons. E-Z configuration. E configuration in which same atoms are on the opposite and in Z- configuration same atoms are on same side.
2.Optical isomerism: The type of isomerism in which isomers are mirror images of each other.