Question

which element will form the ion with the largest ionic radius?

Explanation:

Step1: Recall ionic - radius trend

Ionic radius increases down a group in the periodic table for ions of the same charge. These elements (Mg, Ca, Sr) are in Group 2 and form \(M^{2 +}\) ions.

Step2: Compare the positions

Mg is in the third period, Ca is in the fourth period, and Sr is in the fifth period. As we move down the group from Mg to Ca to Sr, the number of electron - shells increases.

Step3: Determine the largest ionic radius

Since Sr is the furthest down the group among the three elements, it will have the largest ionic radius for its \(Sr^{2+}\) ion.

Answer:

Sr