Debye–Hückel screening length ($\xi$)

The Debye–Hückel screening length is the distance over which mobile ions suppress an electrostatic potential in the linearized electrolyte theory.

For fully dissociated electrolytes at the same temperature and solvent permittivity, linear screening theory gives ${\lambda }_D^{-2}\propto {\sum }_i{c}_i{z}_i^2=2I$. A divalent symmetric salt of formula concentration $c$ has $I=4c$, not $c$ or $2c$. ion association and nonideal concentrated-solution effects limit this comparison.