The answer is C because Na2CO3 and NaHCO3 can react with each other to form a basic buffer solution. Na2CO3 is a weak base and NaHCO3 is a weak acid. When they are mixed in equal numbers of moles, they can react to form sodium bicarbonate (NaHCO3) and sodium carbonate (Na2CO3), which can together act as a buffer solution. The bicarbonate ion (HCO3-) and the carbonate ion (CO3-2) can react with hydronium ions (H+) or hydroxide ions (OH-) in the solution, helping to maintain a relatively constant pH.
