计算下列电解质的平均活度(活度系数可自查手册):-|||-(1) _(2)S(O)_(4)(0.5mol/kg);-|||-(2) HCl(0.2mol/kg );-|||-(3) (N(O)_(3))_(2)(0.02mol/kg );-|||-(4) _(4)Fe(CN)_(6)(0.1mol/kg