Question

which reagent is responsible for staining gram - positive bacteria purple?
a) iodine
b) crystal violet
c) safranin
d) 95% ethyl alcohol

Explanation:

In Gram - staining, crystal violet is the primary stain. It binds to the thick peptidoglycan layer in Gram - positive bacteria. Iodine acts as a mordant (fixes the crystal violet), 95% ethyl alcohol is the decolorizer, and safranin is the counter - stain (stains Gram - negative bacteria pink/red).

Answer:

B. Crystal violet