Question

n-butane and isobutane are:
(A) Same compound
(B) Allotropes
(C) Isomers
(D) Structural isomers

Answer 1

We should know about the terms allotropes, isomerism and its types. Also, we should know how to draw the structures, the IUPAC nomenclature of these structures and the common names used for them.

Complete step by step answer:
n-butane has chemical formula ${C_4}{H_{10}}$ and isobutane has chemical formula ${C_4}{H_{10}}$ . So we observe that the chemical formulas for both are the same. Thus, allotropes option is eliminated. Now we will check the order in which they are placed.
Structural formula of n-butane can be written as $C{H_3} - C{H_2} - C{H_2} - C{H_3}$

Whereas, Structural formula of isobutane can be written as $C{H_3} - CH(C{H_3}) - C{H_3}$ . Its IUPAC name is Methylprop-2-ene.

Since the chain varies due to the position of the carbon atom, thus it is an example of a structural isomer.
So, option D. structural isomer is the correct option to the given question.

Note:

Serial number	Allotropes	Isomers
1.	They have different chemical formulas.	They have the same chemical formula.
2.	They are species of the same element. For example, oxygen ${O_2}$ and ozone ${O_3}$ .	They are composed of different elements, for example ${C_4}{H_8}$ is an example of but-1-ene and but-2-ene.
3.	They always have different structures.	They may or may not have the same structures.
4.	It is observed in metals, nonmetals and metalloids.	Isomerism is generally observed in inorganic molecules and hydrocarbons.
5.	We can’t specify the type. For carbon, there are eight allotropes.	Types: structural isomers and stereoisomers.