Final answer:
The stage with the nuclear envelope reassembly, reappearance of nucleoli, and chromosome decondensation is telophase, the last stage of mitosis.
Step-by-step explanation:
The stage that is described by the events of the nuclear envelope reassembling, nucleoli reappearing inside the newly formed nucleus, and chromosomes decondensing is known as telophase. This is the last stage of mitosis, which involves the reformation of the nuclear membranes around the chromosomes that have reached the opposite poles of the cell. The chromosomes unwind and begin to form chromatin, making the genetic material available for directing the cell's activities. The mitotic spindles that played a role in chromosome separation are depolymerized into tubulin monomers to be used in the assembly of cytoskeletal components for the daughter cells. At the end of telophase, the cell has essentially completed the process of mitosis, with two newly formed nuclei, and is ready to divide cytoplasm in the subsequent process of cytokinesis.