What is isomerism? Explain with a suitable example.

(N/A) Isomerism is the phenomenon in which two or more compounds have the same molecular formula but different structural arrangements of atoms.
For example,$n$-butane $(CH_3-CH_2-CH_2-CH_3)$ undergoes isomerization in the presence of anhydrous $AlCl_3$ and $HCl$ gas to form isobutane $(CH_3-CH(CH_3)-CH_3)$.
This occurs because the branched-chain isomer is thermodynamically more stable than the straight-chain isomer.