Answer
$K^{+}$ and $SO_{4}^{-2}$
Work Step by Step
Magnesium and carbonate will react with one another to form a precipitate so that leaves potassium and sulfate as spectator ions due to their solubility.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.