Step 1 In step 1,NaNO2+HCl,0−5∘C used for diazotisation reaction. It will form diazonium salt. Further, it will react with KCN to form cyanobenzene.
Step 2 In step 2,SnCl2 and HCl is a Stephen's reduction reagent. Cyanobenzene reduced to benzaldehyde by SnCl2∕HCl.