Vicinal dibromide Z undergoes double dehydrohalogenation to three C4H4 isomers Steps:

• Hot ethanolic NaOH promotes double E2 elimination from C4H6Br2, yielding C4H4 products.
• Z's two chiral centers enable stereospecific paths to 1-buten-3-yne (achiral) and 1,2-butadiene (chiral allene).
• Elimination across the vicinal Br's in one direction gives 1-buten-3-yne; orthogonal path yields the enantiomeric 1,2-butadienes.
• Total: one achiral + enantiomeric pair = three isomers, with two optical.

Why A is correct:

• A's structure (e.g., 1,2-dibromo-2-methylcyclopropane) has two chiral centers and Br placement allowing exactly these elimination products per Zaitsev rule for alkynes/allenes.

Why the others are wrong:

• B: Yields four stereoisomers, exceeding three.
• C: No chiral centers, so no optical product pair.
• D: Produces only two achiral isomers.

Final answer: A