Question

what is mitosis?
thickening of the cytoplasm
production of the cells energy
division of the nucleus

Explanation:

Mitosis is a process of cell - division in which the nucleus divides into two genetically identical daughter nuclei. The thickening of the cytoplasm is not mitosis. The production of a cell's energy is mainly related to processes like cellular respiration in mitochondria, not mitosis.

Answer:

division of the nucleus