how do u write an electron configuration?

Question

for the number 15 the number 12 the number 9 or the number 18

Answer 1

15=phosphorus
1s2 2s2 2p6 3s2 3p3

12=Magnesium
1s2 2s2 2p6 3s2

9=Flourine
1s2 2s2 2p5

18=Argon
1s2 2s2 2p6 3s2 3p6

Answer 2

what he wrote earliar is the proffesional method of writing the electronic configuration
there are two other ways i learned how to do the same thing in skool...
the first one is 2n^2 ....where 2 is mul by the no of electronic shells used.
For 15 it would be 2mul by the first shell ^2 that would be 2x1^2 which is two...so 2 electrons go on the first shell...u got the pattern rite?i hope so.
the other one is the no of elements in each period of the periodic table...for eg hydrogen and helium are 2 elements...so two electrons are needed in the first shell
u figure out how to write it
i would just write the answer directly