An alkene A gives the compound shown as its only organic product on ozonolysis followed by $\mathrm{H}{}_2\mathrm{O}{}_2$. Which structure is A?

The compound shown is pentanedioic (glutaric) acid. A five-carbon chain with carboxyl groups at both ends comes from cleaving the double bond of cyclopentene, since all five ring carbons are retained. Cyclohexene would give hexanedioic acid, and the two cyclic dienes would each give two different acids (cyclopentadiene gives oxalic and malonic acids).