Question

Al3+ is smaller than Mg2+ although both are isoelectronic

Answer 1

This is because Al has 13 protons while Mg has 12 henceforth attraction in mg is more than Al

Answer 2

Al 3 + is smallest then magnesium because in a periodick table alumuniaum as metal group and Aluminium comes in non metals and nonmetals have a small Didi is due to high electron negativity so the smaller size in both is Al3+