An alkyl halide(X) on reaction with ethanolic sodium hydroxide forms an alkene(Y) which on further reaction with HBr gives the same alkyl halide. The alkene(Y) on reaction with HBr/peroxide followed by reaction with Mg metal followed by reaction with HCN produces an aldehyde(Z) (here consider the reaction between RMgX and HCN is nucleophilic addition not the acid base reaction). Among the following  Z can be