Hi

Answer :- 7 times

EXPLANATION

In Mitosis a cell divides to produce two daughter cells.

So

In the 1st division, 1st cell produces 2 daughter cells

Then,

In the 2nd mitosis, 2 cells produces  4 daughter cells

In the 3rd mitosis, 4 cells give 8 daughter cells

In the 4th mitosis,8 cells give 16 daughter cells

In the 5th mitosis, 16 cells give 32 daughter cells

In the 6th mitosis, 32 cells give 64 daughter cells

In the 7th mitosis, 64 cells give 128 daughter cells

So,  7 mitotic divisions are required to produce 128 cells.

Short trick

Number of times of mitosis a cell will  have to go through by the formula 2^n, where n = the no. of times the cell divides mitotically.

Then 2^n = 128

Or n = 7

Thank you