Final answer:
The correct answer is that bleach requires a minimum of 2 minutes contact time to reliably kill infectious agents. Other options are incorrect as the presence of organic material compromises bleach's effectiveness, the solution is unstable after dilution, and the best dilution ratio can vary.
Step-by-step explanation:
The correct statement about bleach as a disinfectant is that bleach requires a minimum of 2 minutes contact time to reliably kill infectious agents. Option a) is incorrect because bleach's efficacy is compromised by the presence of blood or other organic materials, which can inactivate the hypochlorous acid that is essential for the disinfecting property of bleach. Option b) is also not true, as the stability of bleach after dilution is much shorter than one month; it starts to lose its effectiveness because the compound in the solution is unstable and easily decomposes. Option c) might not always be the best dilution for general disinfection, as the proper dilution can vary based on different circumstances and types of contamination. It's important to follow specific guidelines provided for disinfectant use to ensure the elimination of pathogens.
The use-dilution test is a common method used to measure the effectiveness of chemical disinfectants such as bleach, by applying them on stainless steel cylinders exposed to pathogens and evaluating whether the microbes survive after treatment. Lastly, the effectiveness of chemical disinfectants has historically been compared to that of phenol, as in the Use-Dilution Test.