What is the name of the first stage of mitosis that involves the condensing of chromosome and the disappearence of the nuclear envelope?
The first stage of mitosis that involves the condensing of chromosomes and the disappearance of the nuclear membrane is called prophase.
Mitosis consists of four phases: prophase, metaphase, anaphase, and telophase. The occurrences during each phase are identified within the link that is provided at the bottom of this answer.
Mitosis is a form of cellular division done by somatic cells. Somatic cells are body cells. Examples of somatic cells are skin cells, the cells of the intestinal lining, or muscle cells.
During mitosis, one diploid parent cell is divided into two identical daughter cells that are also diploid. Cells that are “diploid” have the full number of chromosomes that is characteristic for that species. For example, humans have 46 chromosomes. During mitosis of a human somatic cell, one parent cell with 46 chromosomes makes two daughter cells that also have 46 chromosomes.
The number of chromosomes is maintained in mitosis because each chromosome replicates once at the end of interphase. Thus, at the beginning of mitosis, the parent cell contains twice the normal number of chromosomes. The division of this duplicated number of chromosomes into two daughter cells assures that the correct number of chromosomes is maintained generation after generation.