The number of electrons in the outermost shell of an atom determines its reactivity. Noble gases have low reactivity because they have full electron shells. Halogens are highly reactive because they readily gain an electron to fill their outermost shell
Answer:
https://www.enotes.com/homework-help/what-scientific-question-520157
Explanation:
cuz it is (copy and paste)
Answer:
subscript is 3
Explanation:
the subscript is the number that is slightly lower than a # which in this case it's O
this indicates that there's 3 oxygen atoms
