Identify A to D.

Explanation

DU in `(A)=((2xx9+2)-12)/(2)=4^@`
DU in `(B)=((2xx9+2)-18)/(2)=1^@`
1 DU in (B) suggests there is a ring in both (B) and (A).
Formation of two isomeric ketones (C and D) from A shows internal alkyne of the type `R^'-C-=C-R^'`, which requires at least four C atoms outside the ring. Total C atoms in `(A)=9`.
C atoms required for internal alkyne outside the ring `=4`.
Therefore, ring must be five membered `(9-4=5)`.
4 DU in (A) can be accounted for: 1 DU (ring) + 2 DU `(C-=C)+1 DU` for one `(C-=C)` which must be inside the ring.
Therefore, possible structures of A are:


From the oxidative cleavage of (I), (II), and (III), it is clear that the products of oxidation from (I) are same as given in the problem. So the structure of (A) is (I).
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