D except for the transition metals copper iron tantalum etc they have different oxidation states so arent fixed shells but all main group elements are grouped by the valence electrons sodium potassium lithium alkali column 1 valence electron highly reactive.
Answer:
They were formed right after the "Big Bang" when our known universe originated from pure energy some billions of years ago. The energy was converted to the elementary particles (quarks, gluons, leptons etc...) from which protons and neutrons were formed. From these, atoms of different elements were produced
Answer:
4.21
Explanation:
use Avogadro's number
6.023 x 10^23
multiply this by 7 because you want to find 7 moles :
6.023 x 10^23 x 7 = 4.21
