Hi :)
The bottom number tells you how many protons you have in the nucleus of this element.
In Krypton-84, this means that you have 84 nucleons, where 36 of these are protons, and the remaining 48 are neutrons.
Hope this helps :)
Because those can leak and cause cancer
D ................................
It is made of only nonmetals is not true because there are other elements that form it.
