Which microscope part would help Charles see the most detail of the onion cell?

The microscope part that would help Charles see the most detail of the onion cell is the objective lens with the highest magnification. Most light microscopes are equipped with several objective lenses that can be rotated into place to change magnification. Typically, these lenses may have magnifications of 4x, 10x, 40x, and 100x (oil immersion lens). To achieve the highest level of detail (also known as resolution), Charles should use the 100x oil immersion lens, if available. However, since handling the oil immersion lens requires more skill and it may not be necessary for viewing onion cells, the 40x objective lens might be sufficient and more practical for a clear, detailed look at the cell structure. It’s important that Charles also adjusts the focus using the fine adjustment knob and ensure the illumination is optimal for the magnification he chooses.