How many mitotic divisions cell needed for a single cell to make $128$ cells?

Mitosis is a process of nuclear division in eukaryotic cells that occurs when a parent cell divides to produce two identical daughter cells.

Hence the process of the division will be:

1 cell gives 2 daughter cells (1st mitosis)

2 cells give 4 daughter cells (2nd mitosis)

4 cells give 8 daughter cells (3rd mitosis)

8 cells give 16 daughter cells (4th mitosis)

16 cells give 32 daughter cells (5th mitosis)

32 cells give 64 daughter cells (6th mitosis)

64 cells give 128 daughter cells (7th mitosis)

Hence 7 mitotic divisions cell needed for a single cell to make 128 cells.