For the reaction:

H2PO4- + HAsO42- ---> HPO42- + H2AsO4-

Which pair exists as base in the equilibrium?

H2PO4- & H2AsO4- are proton donors,therefore they are conjugate acids. HPO42- & HAsO42- are proton acceptors,therefore they are the base pairs asked in the question.Is it correct Dr.Bob? Need ur confirmation,help pleaaaaaaaaseeee
Thank you