Answer:
(2) the same molecular formula and different properties
Step-by-step explanation:
Butane and methylpropane are both isomers.
Isomerism signifies the existence of two or more compounds with different molecular structure but having the same molecular formula.
The structural difference is as a result of arrangement of the atoms or the orientation of the atoms in space.
Compounds differing in their structures but having the same molecular formula are called isomers. Isomers like butane and methylpropane differs in both their physical and chemical properties.