Their cells have a very well defined nucleus ,in which nuclear material (chromosomes or DNA) is enclosed in double nuclear membrane.

Prokaryotes
Bacterial
Viral
Eukaryotes

The correct answer is: Eukaryotes.

Eukaryotes are cells that have a well-defined nucleus, in which nuclear material (chromosomes or DNA) is enclosed in a double nuclear membrane. This distinguishes them from prokaryotes, which do not have a nucleus. Eukaryotes also have other organelles, such as mitochondria and chloroplasts, which are not found in prokaryotes.

Bacteria are prokaryotes. They do not have a nucleus, and their DNA is not enclosed in a nuclear membrane. Instead, their DNA is found in a region of the cell called the nucleoid. Bacteria also do not have other organelles, such as mitochondria and chloroplasts.

Viruses are not cells. They are made up of a protein coat that surrounds a nucleic acid core. The nucleic acid can be either DNA or RNA. Viruses cannot replicate on their own, and they must infect a host cell in order to replicate.

Therefore, the correct answer is Eukaryotes.