17. describe how methylene blue can be used to check the effectiveness of an antiseptic or disinfectant. ( /2)

Brief Explanations:

Methylene blue is a redox - indicator. In the presence of viable bacteria (which can be inhibited by antiseptics or disinfectants), it gets reduced and changes color. If an antiseptic or disinfectant is effective, there will be fewer viable bacteria, less reduction of methylene blue, and less color change.

Answer:

Methylene blue is a redox - sensitive dye. Bacteria can reduce it. When an antiseptic or disinfectant is effective, it reduces the number of viable bacteria. With fewer viable bacteria, less methylene blue is reduced, resulting in less color change. So, by observing the color change of methylene blue in a sample treated with an antiseptic or disinfectant compared to a control, one can assess the effectiveness of the antiseptic or disinfectant.