**Explanation:**

The correct answer is **c) Robert Brown**.

**Robert Brown:**
Robert Brown was a Scottish botanist who made significant contributions to the field of botany. In 1827, while studying plant cells under a microscope, Brown observed a distinct structure inside the cells of orchid plants. This structure appeared as a small, dense, and centrally-located body. He named this structure the "nucleus," derived from the Latin word for "kernel" or "seed." This discovery marked the first documented observation of nuclei.

**Nuclei:**
Nuclei are membrane-bound organelles found in eukaryotic cells. They are often referred to as the "control center" of the cell because they contain the cell's genetic material, DNA, and are responsible for regulating cellular activities such as growth, metabolism, and reproduction.

**Robert Brown's Observations:**
Robert Brown's observations were made possible by the advancements in microscopy during the early 19th century. He used a compound microscope to examine plant cells, and it was during these observations that he noticed the presence of the nucleus. Brown's discovery of the nucleus was significant because it provided evidence for the existence of a distinct, organized structure within cells. This finding laid the foundation for further research into the structure and function of cells.

**Impact and Significance:**
The discovery of nuclei by Robert Brown had a profound impact on the field of biology. It opened up new avenues of research into the organization and functioning of cells. Subsequent studies revealed that nuclei play a crucial role in various cellular processes, including DNA replication, gene expression, and cell division.

**Conclusion:**
In conclusion, nuclei were first discovered by Robert Brown, a Scottish botanist, in 1827. His observations of plant cells under a microscope led to the identification of a distinct, centrally-located structure, which he named the nucleus. This discovery marked a significant milestone in the understanding of cellular structure and function.

Discovery of cell nucleus:-- Robert brownExplaination:-Robert Brown studied nearly 1700 plant species and other notable observations include the identification of naked ovule of the gymnospermae.While he was scrutinizing the epidermis of a collection of orchids with his microscope, Brown found that the cells contained an opaque spot. He used the term areola to describe them. They had been seen by other scientists previously who most likely regarded them as insignificant.But Robern brown was not to ignore this specific observation and he further noted that the spot was not limited to epidermis as it could also observed during the early stages of pollen grain formation. He sensed that this spot was a key component of cells & called them " Nucleus" _ a term which is still being used today.