This is a chemical element. You can find the how many electron in a single atom by using a Periodic Table.
An oxygen atom has two shells. The first contains two electrons, and the second contains six electrons.
46
Magnesium has three electron shells. The electron configuration is 2,8,2
There are 8 electrons. 2 in the 1st shell and 6 in the 2nd.
Uranium has 92 electrons, which means it has 7 electron shells.
Berkelium has 97 electrons, which means it has 7 electron shells.
Chromium has two electrons in the outer most shell.
Nickel has 3 (three) electron shells.
2
A neutral xenon atom has 54 electrons. Two of its electron shells would be completely filled, with 2 and 8 electrons, leaving 44 electrons in the remaining electron shells.
Beryllium has 2 electron shells.
Nitrogen has 7 electrons, oxygen has 8 electrons, and chlorine has 9 electrons. That is the total electron count, for inner and outer shells. If you are only concerned with the valance electrons, then it is 5 for nitrogen, 6 for oxygen, and 7 for chlorine.