Sodium carbonate in aqueous solution is

A solution of sodium carbonate in water is

Why sodium carbonate solution is alkaline ?

Consider the following salts : Sodium sulphate, Sodium carbonate, Ammonium sulphate The aqueous solution of which of these salts will: turn phenolphthalein to pink ?

Consider the following salts : Sodium sulphate, Sodium carbonate, Ammonium sulphate The aqueous solution of which of these salts will: turn China rose indicator to green ?

Consider the following salts : Sodium sulphate, Sodium carbonate, Ammonium sulphate The aqueous solution of which of these salts will: turn blue litmus to red ?