Which two elements have the same number of filled energy levels? 1) He and Ne 2) Na and Cl 3) O and S 4) Be and Al

The number of energy levels corresponds to the location of the chemical element in the periodic table.
1) He – helium is located in 1 period, 1s2; Ne – neon is located in period 2, 1s2 2s2 2p6.
2) Na – sodium is located in the 3rd period, 1s2 2s2 2p6 3s1; Cl – chlorine is located in the 3rd period, 1s2 2s2 2p6 3s2 3p5.
3) O – oxygen is located in the 2nd period, 1s2 2s2 2p4; S – sulfur is located in the 3rd period, 1s2 2s2 2p6 3s2 3p4.
4) Be – beryllium is located in the 2nd period, 1s2 2s2; Al – aluminum is located in the 3rd period, 1s2 2s2 2p6 3s2 3p1.
The filled energy level is the level where all electrons are present and are paired.
For the first level it is 2 electrons, for the second – 8 electrons, for the third – 18 electrons.
Sodium and chlorine are located in the same period, have 3 energy levels, and they have 2 complete levels.
Answer: 2) Na and Cl.