Question

Site of formation of ribosomal precursor or ribosomal subunits in a cell 
(A) Nucleus
(B) Nucleolus
(C) Nucleus body
(D) Stroma

Answer 1

Hint: The site of formation of ribosomal precursor or ribosomal subunits in a cell is the largest structure in the nucleus of the eukaryotic cell. It is composed of RNA and proteins and transfers genetic information.

Complete step by step answer:
In a cell nucleolus is the site of the formation of ribosomal precursor or ribosomal subunits. The nucleus is the organelle containing the nucleolus and the nucleus is present in semi-viscous fluid i.e matrix which is present in the cell and is surrounded by the cell membrane. Primarily, it participates in assembling the ribosomes, alteration of transfer RNA, and sensing cellular stress. The nucleolus consists of RNA and proteins which form around specific chromosomal regions.
So, the correct answer is ‘Nucleolus’.

Additional Information: Three major components of the nucleolus are recognized: the fibrillar center (FC), the dense fibrillar component (DFC), and therefore the granular component (GC). Transcription of the rDNA occurs within the FC. The DFC contains the protein fibrillarin, which is vital in rRNA processing. The GC contains the protein nucleophosmin, which is additionally involved in ribosome biogenesis.However, it's been proposed that this particular organization is merely observed in higher eukaryotes which evolved from a bipartite organization with the transition from amniotes to amniotes. Reflecting on the substantial increase within the DNA intergenic region, an original fibrillar component would have separated into the FC and therefore the DFC.

Note: The nucleolus was identified by using bright-field microscopy during the year 1830. The nucleolus is an organelle, and an unusual one because it's there is the absence of lipid bilayers, which are characteristic of other organelles.