Organisms with no nucleus in their cell are called prokaryotes (eg: bacteria and archaea). Bacteria are unicellular organisms and they have only one circular chromosome attached to the plasma membrane and it does not contain any defined nucleus.
The eukaryotic nucleus and animal cell nucleus are same.
Thus, the options (b), (c) and (d) are incorrect.
Organisms with no nucleus in their cell are called prokaryotes (eg: bacteria and archaea). Bacteria are unicellular organisms and they have only one circular chromosome attached to the plasma membrane and it does not contain any defined nucleus.
Therefore, the correct option is – a. prokaryotic cell.