According to Freundlich isotherm, the amount of gas adsorbed(x) per unit mass of solid adsorbent (m) is related with pressure(P) at a particular temperature is given by:

x/m = k.P^1/n ( n > 1)

So, log(x/m) = 1/n.logP + logk ……..(equation-I)

So if we plot log(x/m) on y-axis and vs. logP in x-axis, it comes to be a straight line only.

If 1/n = 0, log(x/m) = logk, so adsorption becomes independent of pressure. So (i) is correct but (ii) is wrong.

When n = 0, then x/m becomes a constant and the Freundlich isotherm is not followed. So x/m vs p graph is a line parallel to x-axis, then (iii) is correct.

If n = 0, then plot of x/m vs. P will not be curve since it will be a straight line. So (iv) is wrong.