There are: 21/3 = 7
7
The are two electrons in the 3s orbital of magnesium (Mg.)
It could be: 33-(3+3) = 21
28 3s
its clearly 8 3 6 9 12 15 18 21 4
0.1429
To find out how many 3s go into 140, divide 140 by 3. This gives you approximately 46.67. Since we're looking for whole 3s, you can fit 46 complete 3s into 140.
16
9
4
37.6666667
2,560