The central cytoplasmic region of a prokaryotic cell containing nucleic acids is called :

Prokaryotic cells (such as bacteria and archaea) are characterized by the absence of a membrane-bound nucleus. Instead, their genetic material—typically a single, circular double-stranded DNA molecule—is concentrated in an irregularly shaped, non-membrane-enclosed region within the cytoplasm called the nucleoid.

• Nucleus: A membrane-bound organelle that houses the genome in eukaryotic cells; it is absent in prokaryotes.
• Nucleolus: A dense structure located inside the eukaryotic nucleus responsible for ribosome synthesis.
• Plastids: Double-membrane organelles (like chloroplasts) found in plants and algae, used for photosynthesis or storage, and are not present in prokaryotic cells.

Therefore, the nucleoid is the functional equivalent of a nucleus in prokaryotes but lacks the surrounding nuclear envelope.