Part (i): starting from benzene.
Step 1: Treat benzene with fuming/concentrated \(H_2SO_4\) so that an \(-SO_3H\) group replaces a ring hydrogen: \( C_6H_6 + H_2SO_4 \rightarrow C_6H_5SO_3H + H_2O \).
Step 2: Fuse the benzenesulphonic acid with excess solid NaOH; alkali fusion converts \(-SO_3H\) into \(-ONa\): \( C_6H_5SO_3H \xrightarrow{NaOH,\ \Delta} C_6H_5ONa \).
Step 3: Acidify with dilute HCl to liberate phenol from its sodium salt: \( C_6H_5ONa + HCl \rightarrow C_6H_5OH + NaCl \).
Part (ii): starting from aniline.
Step 4: Diazotise aniline with \(NaNO_2\) and HCl kept ice-cold at 0 to 5 \(^{\circ}\)C: \( C_6H_5NH_2 \xrightarrow{NaNO_2/HCl,\ 273-278\,K} C_6H_5N_2^{+}Cl^{-} \).
Step 5: Boil the diazonium salt with water; hydrolysis replaces the diazonium group by \(-OH\) and evolves nitrogen: \( C_6H_5N_2^{+}Cl^{-} + H_2O \xrightarrow{\Delta} C_6H_5OH + N_2 + HCl \).
\[\boxed{\text{Benzene}\rightarrow C_6H_5SO_3H\rightarrow C_6H_5ONa\rightarrow C_6H_5OH;\ \ \text{Aniline}\rightarrow C_6H_5N_2^{+}Cl^{-}\rightarrow C_6H_5OH}\]