Predict the most stable ion for these elements, largest to smallest radius?

Question

3 part?
1.which ion out of Na,Mg,Al,S,Cl,K,Ca, and Ga is the most stable

2.arrange these elements from LARGEST to SMALLEST radius

3.explain why the radius varies as it does

thanks for the help!!!

Answer 1

the most stable also means the less reactive.
thus for part 1,
i think it is Cl. but im not very sure.

for part 2 & 3.
im lazy to check them out one by one but i'll explain to you how its done.

look at the periodic table for their respective proton numbers.
which also indicates the number of electrons they have since no. of electrons = no. of protons.

the more layers of electrons, the larger its radius..
for e.g. an element with an electronic configuration of 2.8.6 means it has 3 layers of electrons
whereas 2.4 means it has 2 layers of electrons.
so obviously the former has a larger radius.
u can think of it like a circle, and the radius is therefore the "distance frm the inner layer to the outer layer"

hope that helps :)