(1)H 2(2)H 2O
(3)②④
(4)2NaC1+2H 2O==2NaOH+H 2↑+C1 2↑
2Ca(OH) 2+2C1 2=Ca(C1O) 2+CaC1 2+2H 2O
Ca(OH) 2+CO 2=CaCO 3↓+H 2O