C4H8 Isomers with π Bonding Steps:

• Determine degree of unsaturation for C4H8: (2C + 2 - H)/2 = 1, indicating one π bond or ring.
• Identify acyclic alkenes with π bonds: 1-butene (1 structure), 2-butene (cis and trans stereoisomers, 2), 2-methylpropene (1), totaling 4.
• Identify cyclic structures with π bonds: cyclobutene (1, ring with endocyclic double bond), methylenecyclopropane (1, ring with exocyclic double bond), adding 2 more.
• Exclude saturated rings like cyclobutane and methylcyclopropane, as they lack π bonds; total isomers with π bonding: 6.

Why D is correct:

• C4H8 has exactly six isomers featuring π bonds (in double bonds), including structural and stereoisomers as specified.

Why the others are wrong:

• A: Underestimates by ignoring stereoisomers and cyclic π structures.
• B: Captures only the four acyclic alkenes, missing two cyclic π compounds.
• C: Counts five, likely omitting one stereoisomer or cyclic isomer.

Final answer: D