I think the answer will be b cuh
Just remember how many electrons can each sublevel hold.
S=2
P=6
D=10
Since we have 10 for atomic number, we can assume we have 10 electrons
1S2
2S2
2P6
The rest have zero because we already have 10 (2+2+6=10)
3rd one:
it is very reactive because it does not have a full Valence shell.
this is because it's in group 1 so it has one electron in its outer shell, and it wants to have a full outer shell ( which it can gain by losing the electron in a reaction).
Hope this helps :)
