For a strong electrolyte, at high concentration, the number of constituent ions of the electrolyte in a given volume is high and hence the attractive force between the oppositely charged ions is also high. The ions also experienced a viscous drag due to greater solvation. These factors attribute for the low molar conductivity at high concentration.
When the dilution increases, the ions are far apart and the attractive forces decreases. At infinite dilution, the ions are so far apart, the interaction between them becomes insignificant and hence the molar conductivity increases and reaches a maximum value at infinite dilution.
