The halide shown is converted to its Grignard reagent with magnesium in dry ether; benzonitrile ($\mathrm{C}{}_6\mathrm{H}{}_5\mathrm{CN}$) is added, and the mixture is then heated with aqueous acid. Which structure is the final product?

The Grignard reagent adds once to the polarised C#N bond to give a magnesium imine salt (it cannot add again because the anion is unreactive); aqueous acid hydrolyses the imine to a ketone. Butylmagnesium bromide therefore gives valerophenone (1-phenylpentan-1-one). The amine is a reduction product, the secondary alcohol would come from benzaldehyde, and the acid from hydrolysis of the nitrile alone.