K + H2O = MgO + HCl = NaOH + H2SO4 = Li2O + H2O =
1) 2K+2H₂O=2KOH+H₂↑; 2) MgO+2HCl=MgCl₂+H₂O; 3) 2NaOH+H₂SO₄=Na₂SO₄+2H₂O; 4) Li₂O+H₂O=2LiOH.