Final answer:
A milky appearance on microscope slides after staining is usually due to air bubbles or excess mounting medium, which can be resolved by gently rocking the slide and letting it sit undisturbed.
Step-by-step explanation:
When microscope slides have a milky appearance after staining and cover slipping, the most likely cause is the presence of air bubbles or excess mounting medium. To remedy this issue, you can gently rock the slide back and forth for 1 minute to help disperse any air bubbles. Afterward, let the slide sit undisturbed for an additional minute on the lab bench. Observing the slide without moving it again should allow you to check for the presence of clumping, which can indicate whether the issue has been resolved. If the problem persists, you may need to carefully remove the cover slip and reapply the mounting medium, ensuring that you eliminate any excess before placing the cover slip back on the slide.