Answer
Since the carbonate ion is a stronger Lowry-Bronsted base compared to Magnesium, $CO_{3}^{2-}$ ion reacts with Hydrogen of water to form $H_{2}CO_{3}$ and $OH^{-}$ ion of water reacts with $Mg^{2+}$ ion to form $Mg(OH)_{2}$:
$CO_{3}^{2-} (aq) + Mg^{2+} (aq) + 2H_{2}O → H_{2}CO_{3} + Mg(OH)_{2}$
Work Step by Step
Given above.