Atomic number of Calcium "Ca" is 20.
We know that there are four quantum numbers which can be assigned to "describe" any electron in an atom. Each electron has a unique set of these four quantum numbers.
n = principal quantum number, which defines the energy level of the electron.
l = azimuthal (angular) quantum number defining the energy sub-level. Its values range from 0 " to " (n-1); 0=s, 1=p, 2=d, 3=f
m(l) = magnetic quantum number indicating orbital within a sublevel. Range from -l" through "0" to "+l
m(s) = spin quantum number. It identifies an electron within an orbital and can have either of the two values +1/2 and -1/2
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The electronic configuration of calcium is:
1"s"^2; 2"s"^2, 2"p"^6; 3"s"^2, 3"p"^6; 4"s"^2 or ["Ar"] 4"s"^2
it is evident that the 19th electron goes to 4"s" energy level.
As such for it n=4, l=0
We know that for l=0, m(l)=0 only.
Hence magnetic quantum number m(l) of 19th electron of calcium is =0
