ionic radius increases down a group. which ion will have the smaller radius? magnesium mg+2 calcium ca+2

Explanation:

Step1: Recall ionic - radius trend

Ionic radius increases down a group in the periodic table.

Step2: Locate elements

Magnesium ($Mg$) and calcium ($Ca$) are in the same group, with magnesium above calcium.

Step3: Determine smaller - radius ion

Based on the trend, the ion of the element higher in the group has a smaller ionic radius. So, $Mg^{+2}$ has a smaller radius than $Ca^{+2}$.

Answer:

$Mg^{+2}$