When an onion peel cell is observed under a compound microscope, the part that can be seen in
Nucleus
The correct option is C:
Explanation of the correct option:
While staining onion peel with methylene blue the stain will be taken by nucleus alone, as it contains genetic material in the form of chromatin material.
Thus, When an onion peel cell is observed under a compound microscope, the part that can be seen is Nucleus.