Isomer count: Determine the maximum number of isomers for the alkene C₄H₈. Consider positional and geometrical (cis–trans) isomerism where applicable. Choose the correct count.

Approach

• Structural isomers: 1-butene, 2-butene, 2-methylpropene.
• 2-Butene exhibits geometric isomerism: cis-2-butene and trans-2-butene.

Count1-butene (1), cis-2-butene (2), trans-2-butene (3), 2-methylpropene (4) ⇒ total = 4.

Final Answer4.