For the mean activity coefficient of the NaOH electrolyte given as defined after the coefficients of the individual ions, for aq. sol. as a function of molality; cf.: D.R. Lide (Editor-in-Chief), CRC Handbook of Chemistry and Physics, Table entitled "Mean activity coefficients of electrolytes as a function of concentration", CRC Press, 2005, p. 5-100 (or other eds.).