Answer:
Do you mean under 2 & 18 or under 4 & 20?
Step-by-step explanation:
2 & 20 are in opposite sections of the periodic table. If you mean 2& 18 the element is Krypton or if you mean 4 & 20 the element is Strontium
2- Helium(He)
20-Calcium(Ca)
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