The compound shown is heated with excess aqueous $\mathrm{NaOH}$ and the cooled mixture is then acidified with $\mathrm{H}{}_3\mathrm{O}{}^{+}$. Which structure is the main organic product?

The compound is methyl 3-cyanopropanoate. Hot aqueous base hydrolyses the ester to the carboxylate and also the nitrile, via the amide, to the carboxylate with release of ammonia. Acidification gives the diacid, succinic acid. Hydrolysis of only the ester would leave the cyano acid, and the amide acid is an intermediate.