Answer:
Prophase
Explanation:
PROPHASE
This is the first phase of mitosis and the *major activity here is the shortening and thickening of the chromosomes*.The *chromosome becomes visible when viewed under light microscope*. *Homologous chromosomes join at the centromere (kinetochore) to become chromatids*. *Mitotic spindle begins to form*, *the nucleolus disappears *and the *nuclear membrane opens up(Nucleus remains intact)*.