The sequence : 1,4,2,3
Further explanation
In an atom there are levels of energy in the shell and subshell
This energy level is expressed in the form of electron configurations.
So the electron configuration shows the number of electrons it has
Atomic number = number of electrons in neutral atoms
Charging electrons in the sub shell uses the following sequence:
1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s², 4d¹⁰, 5p⁶, 6s², etc.
1. 1s² 2s²2p⁶3s²3p⁶4s² : 2+2+6+2+6+2=20
2. 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p³ = 2+2+6+2++6+2+10+3=33
3. 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶ = 2+2+6+2++6+2+10+6=36
4. 1s²2s²2p⁶3s²3p⁶4s²3d⁴ = 2+2+6+2++6+2+4=24