There are several general methods of making salts.
Magnesium sulfate (which is soluble in water) could be made by
Mg(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂(g).
MgO(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂O(l)
Mg(OH)₂(s) + H₂SO₄(aq) → MgSO₄(aq) + 2H₂O(l)
MgCO₃(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂O(l) +CO₂(g)
Hint Mg(OH)2 is insoluble