Which of the following elements has the least tendency to form an ion?
1) Ac
2) As
3) Al
4) Ar
1) Ac
2) As
3) Al
4) Ar
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Ar because it is a noble gas and has a full shell of electrons, it does not want to change it number of electrons. All the other elements strive to achieve a configuration like the noble gases.
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Ar of course, because it is a noble gas, and noble gases are very unreactive, as they have a full outer shell, so they will neither lose electrons or gain them.