According to the question, in a 20 minutes cycle, cells double. In 2 hours i.e 120 minutes there will be 6 cycles of 20 min each. If we start from 10 bacteria, then after 6 cycles of 20 minutes each (2 hours in total), we will have 10x 2^6 cells after 2 hours.So, the correct answer is '2^6 x 10'.