The pair of compounds which cannot exist together in the solution is: A. NaHCO3 and NaOH B. NaHCO3 and H2O C. NaHCO3 and Na2CO3 D. Na2CO3 and NaOH

The correct answer is D. Na2CO3 and NaOH cannot exist together in a solution.

Na2CO3 is sodium carbonate, a salt composed of sodium ions (Na+) and carbonate ions (CO3^2-), while NaOH is sodium hydroxide, an alkali metal hydroxide composed of sodium ions (Na+) and hydroxide ions (OH^-).

When you mix sodium carbonate (Na2CO3) and sodium hydroxide (NaOH) in a solution, a double displacement reaction occurs, leading to the formation of sodium bicarbonate (NaHCO3) and sodium carbonate (Na2CO3):

Na2CO3 + 2NaOH → 2NaHCO3

This reaction consumes sodium carbonate (Na2CO3) and produces sodium bicarbonate (NaHCO3) along with water. So, you cannot have both sodium carbonate and sodium hydroxide together in a solution because they will react with each other to form sodium bicarbonate.