Key Exam Tip:
Remember the key transformations:
• Nitro group reduction to amine: e.g., R-NO$_2 \xrightarrow{\text{Fe/HCl or Sn/HCl}} R-NH_2$.
• Diazotization of primary aromatic amines: R-NH$_2 \xrightarrow{\text{NaNO}_2\text{+HCl, low temp}} R-N_2^+Cl^-$.
• Hydrolysis of diazonium salts: R-N$_2^+X^- \xrightarrow{\text{H}_2\text{O, heat}} R-OH + N_2 + HX$.