Cracking dodecane to balance formulas and check isomerism

Steps:

• Dodecane formula is C₁₂H₂₆; cracking yields alkane X (CₙH₂ₙ₊₂) and alkenes Y, Z (CₘH₂ₘ, CₖH₂ₖ with m ≠ k).
• For statement 1: But-1-ene (C₄H₈) + ethene (C₂H₄) = C₆H₁₂; X = C₆H₁₄ (hexane) balances C₁₂H₂₆.
• For statement 2: But-2-ene (also C₄H₈) + ethene (C₂H₄) = C₆H₁₂; X = hexane balances identically.
• For statement 3: Z as but-2-ene has internal double bond, allowing cis-trans isomerism.

Why D is correct:

• All statements valid: 1 and 2 from formula conservation (C₁₂H₂₆ total), 3 from alkene geometry definition.

Why the others are wrong:

• A wrong: Excludes 2 (but-2-ene same formula as but-1-ene) and 3 (isomerism possible).
• B wrong: Excludes 1 (but-1-ene valid for balance).
• C wrong: Excludes 1 (but-1-ene yields hexane).

Final answer: D