The correct option is B Robert Brown
The cell theory was proposed by two scientists- Schleiden (1838)and Schwann (1839). It says that all the plants and animals are composed of cells and the cell is the basic unit of life. The cell theory was further expanded by Virchow (1855).
Robert Brown observed near-circular spot which was slightly more opaque than the other places. He again observed the same structure in other cells as well. Brown coined the term areola to describe them at first. Although this spot was observed previously by other scientists, Robert understood the significance of this structure and finally named it nucleus.