Reduction of Nitro Compounds

$$\text{R--NO}_2 \xrightarrow{\text{H}_2 / \text{Pd} \quad \text{or} \quad \text{Fe / HCl} \quad \text{or} \quad \text{Sn / HCl}} \text{R--NH}_2$$

(Note: $\text{Fe / HCl}$ is preferred because $\text{FeCl}_2$ formed gets hydrolyzed to release $\text{HCl}$, requiring only a small amount of acid)