This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Phenol test or Reidel Walker test is done to determine: 
Select and explain. 
A. Hardness of water, B. Chlorine demand, C. Quality of disinfectant, D. Efficacy of a disinfectants
D: Efficacy of a disinfectants
Answer: D: Efficacy of a disinfectants 
Explanation: Ans. d. Efficacy of a disinfectants