Final answer:
The reproduction method described is called c) binary fission, where a prokaryotic cell splits into two identical cells after duplicating its DNA and forming a septum.
Step-by-step explanation:
A means of reproduction in which duplicate DNA molecules are separated by cell elongation, followed by the formation of a septum to divide the cytoplasm, is called binary fission. This process of asexual reproduction is typical in prokaryotic organisms, such as bacteria, where the cell's genetic material is a single, circular DNA molecule. Unlike in eukaryotic mitosis, there is no need for complex processes such as karyokinesis because prokaryotic cells do not possess multiple chromosomes or a true nucleus. During binary fission, the DNA is replicated, the cell elongates, a septum forms, and finally, the cell splits into two genetically identical daughter cells.