Which one of these is basic ?

1) CO2 + H2O  → H2CO3 carbonic acid2) SiO2 + H2O → H2SiO3 silisic acid3) Na2O + H2O → 2NaOHThe oxides which on dissolution in water gives basic solution,then such oxides are said to basic oxidesbasic oxides are formed IA & IIA group elements In the given option basic oxides is Na2O.4) SO2 + H2O → H2SO3 sulphorous acidOptions (1),(2),(4) are acidic oxidesThe oxides which on dissolution in water gives acidic solution, then such oxides are said to be acidic oxides. Acidic oxides are formed by non-metalsEg: CO2,SO3,SO2,SO2,SiO2,N2O5,P2O5 etc.