which alkane is the isomer of butane called 2 - methylpropane?

which alkane is the isomer of butane called 2 - methylpropane?
Answer
Brief Explanations:
Isomers have the same molecular formula but different structural formulas. Butane ($C_4H_{10}$) has two isomers: n - butane and 2 - methylpropane (also called isobutane). 2 - methylpropane has a branched - chain structure. The top structure in the image is 2 - methylpropane and the bottom one is n - butane.
Answer:
The alkane that is the isomer of butane called 2 - methylpropane is n - butane.