4. Which of the following are examples of precipitation reactions? Select all that apply.
O 2 H₂(g) + O2(g) → 2 H₂O(1)
O KCl(aq) + AgNO3(ag) → KNO3(aq) + AgCl(s)
O Mg(s) + O2(g) → MgO2(s)
O HCl(aq) + NaOH(ag) → H₂O(1) + NaCl(aq)