Debye–Hückel limiting  law that describes the behavior of strong electrolytes. In explaining  the  non-ideal  behavior  of  strong  electrolytes,  his  mathematical treatment assumes that each ion is surrounded by an ionic  cloud  of  oppositely  charged  ions,  which  retards  the movement of ions in the medium. The theory not only provides a method for calculation of activity coefficients, but has also helped, among other things, in our understanding of diffusion in  ionic  media,  change  in  the  rate  of  ionic  reactions  upon addition of salts,  and biochemical reactions.
Debye and Hückel modified their theory in 1926 and their theory was 
further modified by Onsager. All the postulates of the original theory 
were retained. In 
addition it was assumed that the electric field causes the charge cloud 
to be distorted away from spherical symmetry.
 After taking this into account, together with the specific requirements
 of moving ions, such as viscosity and electrophoretic effects, Onsager 
was able to derive a theoretical expression to account for the empirical
 relation known as Kohlraush's law for the molar conductivity, ?m.

 is known as the limiting molar conductivity, K is an empirical constant and c is the electrolyte concentration Limiting here means "at the limit of the infinite dilution"). Onsager's expression is

where A and B are constants that depend only on known 
quantities such as temperature, the charges on the ions and the 
dielectric constant and viscosity of the solvent. This is known as the 
Debye-Hückel-Onsager equation. However, this equation only applies to 
very dilute solutions.
Thanks & Regard
Aarti Gupta
askiitians Faculty