There is only one 2s orbital in an atom.
25 of them
310.
2000
100 2s for the hundreds digit of 200-30010 2s for the tens digit of 220-23010 2s for the ones digit of 200-300________________________________120 '2s'
Designate the smaller number as s. From the statement of the problem, s + s +12 = 90; or 2s = 90 -12 = 78; s = 39
unknown
1
36
26
42
20 of them.