Why does blowing carbon dioxide gas into aqueous barium hydroxide reduce?

Barium hydroxide is soluble, which signifies that it will produce ions in the solution. Supplementing carbon dioxide will result in a precipitation reaction with Ba(OH)2, which is as follows:  

Ba(OH)₂ (aq) + CO₂ (g) → BaCO₃ (s) + H₂O (l)

As the ions are withdrawn from the solution, there is a reduction in the conductivity, due to this blowing carbon dioxide gas into aqueous barium hydroxide reduce.  

the answer is na (sodium)