Answer:
1) Helium
2) Oxygen
3)Carbon
4) Chlorine
5) Magnesium
Explanation:
Helium has the electron arrangement 2, 2. There are two electrons in the first shell and two electrons in the second shell.
Oxygen is the first member of group 16, there are two energy levels in oxygen which are 2,6.
Carbon is in period 2 and is the first member of group 14 (the silicon family).
Chlorine has 7 valence electrons, the electrons are arranged as 2, 8, 7.
Magnesium has 12 protons and 12 electrons. It is the second member of period 3.