Common ion effect is observed when a solution of weak electrolyte is mixed with a solution of a strong electrolyte, which provides an ion common to that provided by a weak electrolyte.When strong acids such as hydrochloric acid, nitric acid, and aqua regia are added to a solution containing calcium oxalate, the dissociation of oxalic acid is suppressed due to hydrogen ions provided by strong acids (common ion effect). Hence, the concentration of oxalate ions decreases. The precipitate of calcium oxalate will dissolve in it because the product of the concentrations of the ions present in calcium oxalate will be less than the solubility product of calcium oxalate.When acetic acid is added, the common ion effect is not observed, as acetic acid is a weak acid. Hence, the precipitate of calcium oxalate will not dissolve.Option D is the correct answer.