Molar conductivity increases with increase in volume and when volume increases the concentration of solution decreases (because no.of ions in the solution decrease) which makes the solution dilute.
On dilution when concentration approaches zero, the molar conductivity is known as limiting molar conductivity.
In case of strong electrolytes the ionisation is easy and much of electricity is produced. So in the case of strong electrolytes molar conductivity increases on dilution.
When we plot a graph between molar conductivity and C/2 we get a straight line, by extrapolating this line we can get the value of limiting molar conductivity.
But weak electrolytes do not dissociate easily and hence they have low molar conductivity.
On dilution this increases very slowly and becomes almost constant at a point, so extrapolation of this line is not possible and we determine the limiting molar conductivity with the help of Kohlraush law in the case of weak electrolytes.
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