Question

Butane and Isobutane are called Isomers.why?

Answer 1

We find that n-butane and iso-butane have the same molecular formula (C4H10) but they have different structures . They are called as Isomers.
In other words, the organic compounds having the same molecular formula but different arrangement of carbon atoms in them are called as Isomers.
The normal butane has straight chain whereas iso-butane has a branched chain structure.
n-butane:
CH3-CH2-CH2-CH3
IsO-Butane:

CH3-CH-CH3
         Ι
       CH3

Answer 2

the organic compounds having the same molecular formula but different arrangement of carbon atoms in them are called as Isomers. so Butane and Isobutane are called isomers