# Which of the following cations is least likely to form: Sr^(2+), Al^(3+), K^(2+)? Why?

I would say ${K}^{2}$
Cations are ions with positive charges. $K$ is in Group 1 of the periodic table, meaning it only needs to lose 1 electron in order to stabilize - as it has a charge of ${1}^{+}$ Losing two electrons requires a lot of energy from $K$ - meaning that it might not be a spontaneous reaction.