In a study of the electrochromic properties of the system, the cyclic voltammograms accompanying the aqueous electrodeposition of the reduced bipyridilium "cyanophenylparaquat" gave traces specific to the particular anion involved in the deposition. This useful fingerprint is then used to identify which one of a pair of anions in a mixed-electrolyte medium causes the electrodeposition from the mixture. These assignments allow the ranking of anion efficiencies, in a ''dominance" sequence. Here it is shown that the mobility of an anion is the key to its success in deposition, and a diffusion-based rare constant fur initial nucleation is proposed, involving the ionic conductivities of the anions. This conclusion is applicable to singly charged species, the necessarily slower multistep mechanisms required fur 2- cind 4- charge anions being deemed responsible for the lower effectiveness of these reactants.