<prompt> Phenol coefficient indicatesEfficacy of a disinfectantDilution of a disinfectantQuantity of a disinfectantPurity of a disinfectant  <response>: On exposure to air, the colorless crystals of phenol become pinkish and on longer exposure, the color deepens to dark blue. Pure phenol is not an effective disinfectant. It is used as an effective disinfectant. Ref: 25th edition, Parks Textbook of Preventive and Social Medicine, Page no. 140 