Robert brown is known for his discovery of

Mistake Points

• The question is asking about the discovery made by Robert Brown, So according to the option, the correct answer will be Nucleus (Nucleus of the cell). 
• Whereas Ernest Rutherford was the discoverer of Nucleus of Atom.

Concept:

• The term cell was first described by Robert Hooke in the year 1665 in his book called 'Micrographic'.

• A cell is a basic structural & functional unit of life of all existing living organisms.
• A cell consists of different cell organelles like mitochondria, chloroplasts, endoplasmic reticulum, nucleus, etc.
• Every organelle performs a specific function that is required for the proper functioning of the cell.

Explanation:

• Robert Brown, a British Biologist discovered the nucleus in the year 1831.
• This cell organelle was named nucleus according to the Latin word nucleus/ nucleus meaning a seed.
• The study of the nucleus is called Karyology.
• The nucleus is a double membrane-bound dense protoplasmic body, which controls all the cellular metabolism and encloses the genetic information of the cell.
•  The nucleus is considered the controller or director of the cell.

Additional Information

• Golgi complex was discovered by Camillo Golgi in the year 1898. He saw a densely stained reticular structure close to the nucleus.
• These were named Golgy bodies after him.
• Mitochondria were first observed by Kolliker as cytoplasmic granules in stripped muscles of insects.
• Chloroplast was discovered by Hugo von Mohl in 1837, it was named by combining Greek words Chloros (Green) & Plastes ( producer)