Which of the following ions is most likely to form an insoluble sulfate?

Question

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Calcium ion (Ca2+) is a divalent cation with a high charge density and a small ionic radius, which makes it likely to form insoluble sulfates (e.g. CaSO4) with sulfate ions (SO42-). This is due to the strong electrostatic attraction between the calcium cation and sulfate anion, which leads to the formation of a solid precipitate. The other choices (A, B, D, and E) do not have cations with as high a charge density or as small ionic radius as Ca2+, and are therefore less likely to form insoluble sulfates.

Which of the Following Ions Is Most Likely to Form