The correct option is C Not applicable at high pressures
If you remember, we have discussed that the Fruendlich isotherm fails at high pressures of gases. Why you ask?
Well, it just so happens that the equation given by Fruendlich fails to explain what we observe in reality in our experiments. The data we obtain from the experiments doesn't match with the predictions of this isotherm at high pressures.
If you ask why this is, then you will be asking why is reality the way it is. And we don't want to go there! Let's stop here.