Phenol when first reacts with $Conc.H_{2}S{O}_4$ and then with $Conc.HN{O}_3$  it gives

Phenol when first reacts with $Conc.H_{2}S{O}_4$ give phenol -2,4 – disulphonic acid and then with $Conc.HN{O}_3$   gives 2,4,6- Trinitrophenol (Picric acid)