Final answer:
Hematoxylin is the stain used to identify the location of cell nuclei, as it specifically colors the nuclei blue to purple for visualization.
Step-by-step explanation:
The stain used to identify the location of cell nuclei is hematoxylin. This stain is commonly applied in histological studies as part of the hematoxylin and eosin (H&E) stain, where hematoxylin colors the nuclei blue to purple, and eosin stains other cellular structures and cytoplasm in varying shades of pink. Hematoxylin has an affinity for nucleic acids in the nucleus and highlights these structures, allowing for clear visualization under a microscope.