Answer:
6.022 x 10^20 molecules
Step-by-step explanation:
As we know that the number of molecules that are present in one mole of any substance is 6.022 x 10^23. So, if the concentration is 1.0mM, it means it is 1000 times less than a mole. So, simply divide 6.022 x 10^23 by a factor of 1000 or 10^3 and you'll get your answer.