$\text{ Phenol }\stackrel{\text{ conc. }{\mathrm{H}}_2{\mathrm{SO}}_4}{⟶}\mathrm{A}\stackrel{\text{ conc. }{\mathrm{HNO}}_3}{⟶}\mathrm{B}$
Here A and B are respectively

4–Hydroxybenzene–1,3–disulphonic acid, picric acid

P–Hydroxy benzenesulphonic acid, P–nitrophenol

4–Hydroxybenzene-1,3–disulphonic acid, 2,4–dinitrophenol

3–Hydroxybenzenesulphonic acid, picric acid