Answer: 6.02 x 10^25
Explanation:
In order to find the number of molecules you simply multiply the number of moles by 6.022 x 10^23.
1 mole is always equal to 6.022 x 10^23 no matter what element.
100.0 x 6.022 x 10^23 = 6.02 x 10^25
The answer only has three significant figures because 100.0 only has three.