The number of atoms cannot be estimated to that degree of accuracy.
There are exactly 118 known elements. Rounding 118 to the nearest 100 makes it 100.
100.0
122 to the nearest 100 is 100
No. 100 lead atoms are several times heavier than 100 aluminum atoms.
There are not 100 types of atoms.
103 to the nearest hundreds is 100
100
That is 4800
4198 to the nearest 100 = 4200
100
100
100