The biosynthesis of ribosomal RNA occurs in:

The fluid inside the nucleus is called nucleoplasm or nuclear matrix. The nucleoplasm contains nucleolus and chromatin. The nucleolus is a spherical structure. The nucleolus is not a membrane-bound structure. Synthesis of ribosomal RNA ($rRNA$) takes place in the nucleolus. It also participate in the formation of signal recognition particles and play a role in the cell's response to stress. Nucleoli are made of proteins, DNA and RNA and form around specific chromosomal regions called nucleolar organizing regions.