The compound shown is stirred with excess NaOD in $\mathrm{D}{}_2\mathrm{O}$ until exchange is complete. Assume that every hydrogen on a carbon directly bonded to a C=O carbon or to a C$\equiv$N carbon exchanges. How many deuterium atoms are incorporated per molecule?

The compound shown is 3-oxobutanenitrile. The CH${}_3$ group is bonded to the carbonyl carbon (3 H), and the CH${}_2$ group is bonded to both the carbonyl carbon and the nitrile carbon (2 H, the most acidic). The CH${}_2$ hydrogens are counted once, so $3+2=5$ deuterium atoms are incorporated.