Adsorption of a gas follows Freundlich adsorption isotherm. If x is the mass of the gas adsorbed on mass
m of the adsorbent, the correct plot of x/m versus p is :

Solution

Chemistry ma’am · 3 steps

Check two things in every graph: the curve must bend over, and the coldest line must sit on top.

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

2. Shape of the plot. Since 1/n lies between 0 and 1, x/m rises with p but more and more slowly. The plot is a curve that bends towards the pressure axis, not a straight line.
3. Effect of temperature. Adsorption of a gas is exothermic, so by Le Chatelier's principle less gas sticks at higher temperature. At the same p, the 200 K curve must lie highest and the 270 K curve lowest.

   Option	Shape	Highest line	Matches Freundlich?
   (a)	curve, bends over	270 K	no, temperature order reversed
   (b)	curve, bends over	200 K	yes
   (c)	straight lines	200 K	no, wrong shape
   (d)	straight lines	270 K	no, wrong shape and order

4. So. Only (b) shows curves that flatten out with pressure and puts 200 K on top. The answer is (b).

The idea to keep. For Freundlich, x/m against p is a curve because 0 < 1/n < 1. Adsorption is exothermic, so at a fixed pressure the lowest temperature always gives the most adsorption.

Answer from the NTA final answer key. Solution by PrepWiser.