What type of cell division increases the chromosome number by two?

The type of cell division that leads to an increase in the chromosome number by two is mitosis. During mitosis, a single somatic cell divides to produce two genetically identical daughter cells, each with the same number of chromosomes as the original cell. Before mitosis begins, the cell goes through a phase called interphase, during which DNA replication occurs. This replication doubles the chromosome number. Therefore, if a cell starts with a diploid number of chromosomes, upon completing mitosis, each daughter cell will also be diploid, effectively maintaining the same chromosome number.

In the context of the other types of cell division mentioned: meiosis reduces the chromosome number in half as it produces gametes (sperm and eggs), fission is a form of asexual reproduction typically seen in prokaryotes that does not specifically refer to chromosome number changes in the same way as eukaryotic cell division, and "division" is a vague term that does not specify any particular type of cell division. Thus, mitosis is the definitive process by which the chromosome number increases in terms of cell generation, maintaining the genetic integrity during cellular replication.