Which phase of mitosis is characterized by the formation of two new nuclei?

The phase of mitosis characterized by the formation of two new nuclei is telophase. During telophase, the chromosomes, which have been separated into two sets, begin to de-condense back into chromatin. The nuclear envelope re-forms around each set of chromosomes, resulting in the creation of two distinct nuclei within the cell. This process effectively marks the end of mitosis, as the cellular material is prepared for the final separation into two daughter cells.

In contrast, during prophase, the chromosomes condense and become visible, and the nuclear envelope starts to break down, but new nuclei have not yet formed. In metaphase, the chromosomes align at the cell's equatorial plate, and during anaphase, the sister chromatids are pulled apart toward opposite poles of the cell. However, it is in telophase that the newly formed nuclear membranes encapsulate each set of chromosomes, culminating in the establishment of two nuclei in the daughter cells.