Statement Analysis: Aqueous Solutions Properties

Sodium Carbonate Solution Alkalinity

Statement (a) claims an aqueous solution of sodium carbonate ($Na_2CO_3$) is alkaline.

• Sodium carbonate is a salt of a strong base (NaOH) and a weak acid ($H_2CO_3$).
• In water, it dissociates into $Na^+$ and $CO_3^{2-}$ ions.
• The carbonate ion ($CO_3^{2-}$) undergoes hydrolysis:

  $CO_3^{2-}(aq) + H_2O(l) \rightleftharpoons HCO_3^-(aq) + OH^-(aq)$

• This hydrolysis produces hydroxide ions ($OH^-$), increasing the pH and making the solution alkaline.
• Therefore, statement (a) is correct.

Carbon Dioxide Solution Acidity

Statement (b) claims an aqueous solution of carbon dioxide ($CO_2$) is acidic.

• Carbon dioxide dissolves in water to form carbonic acid ($H_2CO_3$):

  $CO_2(g) + H_2O(l) \rightleftharpoons H_2CO_3(aq)$

• Carbonic acid is a weak acid.
• It dissociates in water, releasing hydrogen ions ($H^+$):

  $H_2CO_3(aq) \rightleftharpoons H^+(aq) + HCO_3^-(aq)$

• The presence of hydrogen ions ($H^+$) makes the solution acidic.
• Therefore, statement (b) is correct.

Conclusion

Since both statement (a) regarding sodium carbonate's solution being alkaline and statement (b) regarding carbon dioxide's solution being acidic are correct, the option stating both are correct is the right choice.