An unsaturated hydrocarbon X absorbs two hydrogen molecules on catalytic hydrogenation and also gives following reaction : X→(O₃)A→([Ag(NH₃)₂]⁺) B(3 - oxo - hexanedicarboxylic acid) X will be :-

Solution

Chemistry ma’am · 3 steps

Work backwards: B tells you where the ketone sits, and the ketone tells you where the =CH2 was.

1. Read the clues. Two H₂ absorbed means X has two C=C bonds. Ozonolysis with Zn/H₂O cuts each C=C into two C=O groups. Tollens' reagent then turns only the aldehyde groups into COOH. Ketones are left unchanged.
2. Decode B. B is HOOC-CH₂-CO-CH₂-CH₂-COOH, 3-oxohexanedioic acid. So A must be OHC-CH₂-CO-CH₂-CH₂-CHO. Its two CHO ends came from one C=C inside the ring. The ketone came from a ring carbon carrying an exocyclic =CH₂, which leaves as HCHO.

   Option	Ozonolysis product A	After Tollens (B)
   (a) 1,3-dimethylenecyclohexane	cyclohexane-1,3-dione + 2 HCHO	ring stays closed, no diacid
   (b) 3-methylenecyclohexene	OHC-CO-CH₂CH₂CH₂-CHO	2-oxohexanedioic acid
   (c) 4-methylenecyclohexene	OHC-CH₂-CO-CH₂CH₂-CHO	3-oxohexanedioic acid
   (d) cyclohex-2-enone	OHC-CO-CH₂CH₂CH₂-CHO	2-oxohexanedioic acid, and X is not a hydrocarbon

3. So. In (c), the ring C=C sits two carbons away from the =CH₂ carbon. That places the keto group at C-3 of the six-carbon diacid. X is option (c).

The idea to keep. For ozonolysis puzzles, rebuild the molecule from the product. Join the two C=O carbons that came from the same C=C. An exocyclic =CH2 becomes a ring ketone plus HCHO.

Answer from the NTA final answer key. Solution by PrepWiser.