Answer:
On the placement of hydrogen and helium in the periodic system
H1=1
He2=2
I would say developed technologies which somehow were lost
like the stone age: the stone hammer, who used that afterwards in the roman empire era and stuff?
Answer:
<em>Hydrogen.</em>
Explanation:
You've probably seen "
" which is the formula for water. It means that there's 2 hydrogen atoms, and one oxygen atom, in one molecule of water.
<em>Hope this helps! Feel free to mark me Brainliest if you feel this helped. :)</em>