Arrange `Al^(3+),Na^(+)&Mg^(2+)` ions in the decreasing order of their ionic radii and explain the order.

Explanation

The decreasing order of ionic radii of these three ions is: `r_(Na^(+)) gt r_(Mg^(2+)) gt r_(Al^(3+))`. These three ions are isoelectronic and they contain 10 electrons each in their extra-nuclear shells. Since the magnitude of nuclear charge gradually increases from Na to Al, the nuclear attractive force for the same number of electrons gradually increases. As a result, their ionic radii gradually decreases.