Phenol on treatment with dilute HNO ₃ at room temperature gives a mixture of P and Q . The boiling point of P is lower than that of Q . P on reduction with Sn / HCl yields R . R on reaction with NaNO ₂ and aqueous H ₂ SO ₄ at 0-5 ^ C followed by reaction with an excess of C ₂ H ₅ OD gives S . The structure of S is