stoichiometric mean molal (practical activity coefficient) in electrochemistry

The practical activity coefficient of electrolyte B is given by

$γ ± = a ± ν + ν + ν − ν − m B m +$

where $a ±$ is the mean activity of B in solution, $m B$ is the molality of B, $m + = 1 mol kg −1$ , $ν +$ is the number of cations and $ν −$ the number of anions in the chosen group B which is taken as the electrolyte.

$ν = ν + + ν −$

Source:

PAC, 1974, 37, 499 (Electrochemical nomenclature) on page 510