Which of the following gives cyanide when reacted with KCN (A)...

The reaction with KCN (potassium cyanide) involves an SN1 or SN2 nucleophilic substitution, where the cyanide ion (CN-) replaces a leaving group. (B) Allyl bromide (($\mathrm{CH}$2=$\mathrm{CH}-\mathrm{CH}$2 $\mathrm{Br})$) and (D) Benzyl bromide (($\mathrm{C}$6 $\mathrm{H}$5-$\mathrm{CH}$2 $\mathrm{Br})$) both undergo SN1 or SN2 reactions with KCN to form the corresponding cyanides: - Allyl bromide $→$ Allyl cyanide (($\mathrm{CH}$2=$\mathrm{CH}-\mathrm{CH}$2 $\mathrm{CN}$)) - Benzyl bromide $→$ Benzyl cyanide (C6H5-CH2CN) (A) Chlorobenzene (C6H5Cl) does not react with KCN because the Cl - is not a good leaving group in an aromatic ring. (C) Vinyl chloride (($\mathrm{CH}$2=$\mathrm{CHCl})$) does not undergo SN 1 or SN 2 reactions with KCN due to the stability of the vinyl carbocation and the presence of a chlorine atom bonded to a double bond, making it less reactive. Therefore, only Allyl bromide and Benzyl bromide react with KCN to give cyanide compounds. Hence, option (3) is correct.