Answer:
-Prophase.
Step-by-step explanation:
Cell cycle involves a series of events that leads to formation of two daughter cells by division of a parent cell. It can be divided into two phases, interphase and mitotic phase (M phase)
The M phase involves division of nucleus and cytoplasm to produce two daughter cells. It is divided into prophase, metaphase, anaphase, telophase and cytokinesis.
Hence, the first stage of M phase is prophase, in which condensation of chromosomes begins, nuclear membrane disintegrates, and nucleolus starts to disappear.
Thus, the correct word to be fill in the blank is 'prophase