Provide the classification of isomerism in alkenes with examples.

(N/A) Isomerism in alkenes is classified into two main types: Structural isomerism and Geometrical isomerism.
$1$. Structural Isomerism:
- Chain Isomerism: Alkenes with the same molecular formula but different carbon skeleton structures. Example: $CH_2=C(CH_3)-CH_3$ ($2$-Methylprop-$1$-ene) is a chain isomer of $CH_2=CH-CH_2-CH_3$ (But-$1$-ene).
- Position Isomerism: Alkenes with the same carbon skeleton but different positions of the double bond. Example: $CH_2=CH-CH_2-CH_3$ (But-$1$-ene) and $CH_3-CH=CH-CH_3$ (But-$2$-ene) are position isomers.
$2$. Geometrical Isomerism:
- This arises due to restricted rotation around the $C=C$ double bond.
- Cis-isomer: Similar groups are on the same side of the double bond. Example: Cis-but-$2$-ene.
- Trans-isomer: Similar groups are on opposite sides of the double bond. Example: Trans-but-$2$-ene.