Question

What is the most stable monatomic ion formed from aluminum?

Answer 1

Aluminum is group 13 or IIIA since the group number  12 has the number 3 is the 1st place, we would predict the change to be 3+ to give Al​3+ 

Answer 2

Answer:

The most stable ion is $Al^{3+}$

Explanation:

The aluminium belongs to Group 13 of the periodic table. The elements of this group have 3 electrons of valence and due to the metalic characterictics the aluminuim has, it trends to lose those electrons to achieve stability.  

Electrons are negatively charged (-1 each one), so when the neutral atom loses 3 of them it remains positively charged by +3