Ozonolysis (followed by reductive workup with Zn/H2O) cleaves C=C bonds and converts each alkene carbon into a carbonyl. We can reverse-engineer the parent alkene from the fragments obtained.
Analysing the products:
HCHO (2 moles): Two equivalents of formaldehyde indicate the presence of two terminal or exocyclic =CH2 groups in the parent molecule.
CH3−CO−CO−CH3 (biacetyl): To get this discrete fragment, the parent alkene must contain the structural unit −C(CH3)=C(CH3)−, i.e., an endocyclic double bond in which both sp2 carbons bear methyl substituents.
H−CO−CO−CHO (mesoxaldehyde): This arises from a fragment like =CH−C(=CH2)−CH=, where cleavage of the adjacent C=C bonds generates three consecutive carbonyl groups (and also contributes to the formaldehyde count from the exocyclic =CH2).
Evaluating the options:
The most diagnostic product is biacetyl, so the parent structure must contain the −C(CH3)=C(CH3)− unit.
Option (1): One methyl group is on the endocyclic double bond and the other methyl is on a separate sp3 carbon. Cleavage cannot give biacetyl.
Option (2): Only a single methyl group is present, so biacetyl cannot be formed.
Option (4): The methyl groups lie on opposite ends of the ring (across a 1,4-diene-type arrangement). Ozonolysis would place these methyls in different fragments, so biacetyl cannot be formed.
Option (3): The left side of the ring contains an endocyclic double bond in which both carbons carry methyl groups, giving exactly the required −C(CH3)=C(CH3)− arrangement. Cleavage of this bond together with the adjacent ring double bonds releases a discrete CH3−CO−CO−CH3 fragment. The right side of the molecule carries exocyclic =CH2 groups, which on cleavage produce the two moles of HCHO, while the intervening carbons give rise to H−CO−CO−CHO.
Hence, the correct structure that yields all three ozonolysis products is option (3).