Which of the following elements would most likely lose an election to fill its outermost shell?

The metals are the elements that more easily can lose electrons to fill their outermost shell. And among the metals the alkalyne are most likely than alkalyne earth and these are most likely than other metals.

As less electrons the metal has in its outermost shell the more likely it will lose an electron fo fill its outermost shell.

So, Li, Na, K, Rb, Cs, and Fr have one electron in their outermost shell, so they are more likely to lose an electron to fill their outermost shell than Be, Mg, Ca, Sr, Ba, Ram which have two electrons in their outermost shell.

Using the same reasoning, Be, Mg, Ca, Sr, Ba, Ra are more likely to lose an electron to fill its outermost shell than Al, Ga, In, Tl.

Al, Ga, In, Tl are more likely to lose an electron than Si, Ge, Sn, Pb.

Si, Ge, Sn, Pb are more likely to lose an electron than O, S, Se, Te, Po

O, S, Se, Te, Po are more likely to lose an electron than F, Cl, Br, I, At

F, Cl, Br, I, At (halogens) and He, Ne, Ar, Kr, Xe, Rn (noble gases) will not likely lose electrons.