The practical activity @C01124@ of electrolyte B is given by \[\gamma _{\pm }=\frac{a_{\pm }}{\sqrt{\nu _{\text{+}}^{\nu _{\text{+}}}\ \nu _{\text{-}}^{\nu _{\text{-}}}}\ \frac{m_{\text{B}}}{m^{\text{+}}}}\] where \(a_{\pm }\) is the mean activity of B in solution, \(m_{\text{B}}\) is the @M03970@ of B, \(m^{\text{+}} = 1\ \text{mol kg}^{-1}\), \(\nu _{\text{+}}\) is the number of cations and \(\nu _{\unicode{x2013}}\) the number of anions in the chosen group B which is taken as the electrolyte. \[\nu = \nu _{\text{+}}+\nu _{\text{-}}\]