Answer : The correct option is, (3)
Explanation :
Isomers : It is defined as the molecule that has the same chemical formula but it has the different structures.
Same chemical formula means that the same number of elements are present in both the compounds.
In option 1,2 and 4, both chemical formula and the structure are different. So, the option 1 compounds are not the isomers of each other.
In option 3, the chemical formula is same but the structure are different. So, the option 3 compounds are the isomers of each other.
Hence, the correct option is, (3)