Question

n-butane and isobutane are a pair of
A.Chain isomers
B.Position isomers
C.Metamers
D.Functional isomers

Answer 1

Hint: Constitutional or structural isomers are those isomers which differ from each other due to the arrangement of atoms within the molecule. The various structural isomers are chain isomers, position isomers, ring chain isomers, functional isomers, metamers and tautomers.

Complete step by step solution:
Chain isomerism – This type of isomerism occurs due to the difference in nature of the carbon chain (based on whether it is straight or branched) which gives a basic structure to the compound.
Examples: n-pentane, isopentane, neopentane.

Position isomerism – This type of isomerism is exhibited by compounds in which there is a difference in the position of the substituted group or an unsaturated linkage in the same carbon chain.
Examples: $2,2-\text{dichloropropane, 1,1 - dichloropropane}$.

Metamerism – Metamers are isomers which differ from each other due to the difference in nature of the alkyl group attached to the polyvalent atoms or functional group. They belong to the same homologous series. Some compounds which exhibit metamerism are ethers, ketones, thio-ethers, secondary amines etc.
Examples: $\text{pentan - 2 - one, pentan - 3 - one}$.

Functional isomerism – This type of isomerism occurs due to the difference in nature of functional groups present in the isomers. Some compounds which exhibit functional isomerism are alcohols and ethers, aldehydes and ketones etc.
Examples: Ethyl alcohol, dimethyl ether.
The structures of n-butane and isobutane are:

 

From the structures, it is clear that n-butane and isobutane differ in the skeletal carbon chain. So, they are chain isomers.

Hence, option (A) is the correct answer.

Note:
Isomers are organic compounds having the same molecular formula but different structures or at least some different physical or chemical properties. The difference in properties is mainly due to the difference in relative arrangements of various atoms or groups present in the molecules.