Staining is a technique used to enhance the color contrast of the microscopic samples when observed in the microscope especially in the microbiological samples.
In the given question, when the staining technique is used to identify the sample then staining procedure is followed in a process where the samples can be identified on the basis of the color contrast which is in the case of gram staining.
The gram staining is used to identify the bacteria on the basis of color as the bacteria which appear blue in color are called gram-positive and the bacteria which appear red in color are gram-negative bacteria.
I believe the correct answer would be metabolism. This comprises all of the reactions inside organisms that allows them to sustain life. There are two categories of such namely, anabolism and catabolism. Hope this answers the question.
