Mitosis is split into 4 phases.
P - prophase
M - metaphase
A - anaphase
T - telophase
During Metaphase, Chromosomes align singly along the metaphase plate.
During Anaphase, kinetochore microtubules shortens and non-kinetochore microtubules lengthens, allowing the chromosomes' centromeres to separate.
Therefore, the answer is anaphase.
P. S. centromeres separates, not split.
During the mature stage this happens because the air becomes more dense.
