Answer:
The correct answer would be the nucleus.
A nucleus is a membrane-bound cell organelle only found in eukaryotic cells.
The membrane of the nucleus is termed as nuclear membrane and the gel-like content inside the nucleus is termed as nucleoplasm.
The nucleus is the controlling center of the cell as it contains DNA or genetic material of the cell.
In contrast, prokaryotic cells are primitive cells which lack membrane-bound organelles like the nucleus, mitochondria, Golgi body et cetera. The DNA of a prokaryotic cell remains suspended in the cytoplasm.