• Nucleus as a cell organelle was first described by Robert Brown as early as 1831 . • Later the material of the nucleus stained by the basic dyes was given the name chromatin by Flemming. • Ribosomes are the granular structure first observed under the microscope as dense particle by George Palade. • Camillo Golgi first observed densely stained reticular structure near the nucleus. It consist of many disc shaped sac or cisternae. Hence, A-II, B-IV, C-III, D-I is correct.