A sample may contain any or all of the following ions: Hg2 2, Ba2, and Mn2.
a. No precipitate formed when an aqueous solution of NaCl was added to the sample solution.
b. No precipitate formed when an aqueous solution of Na2SO4 was added to the sample solution
c. A precipitate formed when the sample solution was made basic with NaOH.
Which ion or ions are present in the sample solution?