After conducting the gram stain on a mixed culture containing gram-positive rods and gram-negative cocci, all the cells were purple in color. this was most likely because

the cells were not decolorized enough with alcohol or acetone.

Explanation:

The preparation of Gram stain on a mixed culture containing Gram-positive rods and Gram-negative cocci as they are used in the staining procedure can be crystal violet, iodine, ethanol/acetone and safranin. The initial reaction of the staining procedure is with the addition of the primary stain, crystal violet, to the bacterial smear. Crystal violet colors the bacterial cell purple. Now, if After conducting the Gram stain on a mixed culture containing Gram-positive rods and Gram-negative cocci, all the cells were purple in color. This was most likely because the cells were not decolorized enough with alcohol(ethanol) or acetone.