Question

which reagent is used as a counterstain?
a) crystal violet
b) iodine
c) 95% ethyl alcohol
d) safranin

Explanation:

• Crystal violet is the primary stain in Gram - staining.
• Iodine is a mordant in Gram - staining.
• 95% ethyl alcohol is a decolorizer in Gram - staining.
• Safranin is used as a counterstain in Gram - staining. It stains the Gram - negative bacteria (which have lost the crystal violet - iodine complex after decolorization) pink or red.

Answer:

d) Safranin