Which of the following represent the Freundlich adsorption isotherms?
Choose the correct answer from the options given below:

Solution

Chemistry ma’am · 2 steps

Write x/m = k p^(1/n) first, then check each graph's axes against it.

1. The equation. Freundlich says the amount adsorbed per gram rises as a fractional power of pressure, with n > 1. Its log form is a straight line.

   x/m = k p^(1/n) ⇒ log x/m = log k + 1/n log p

   Graph	Axes	What Freundlich predicts	Matches?
   A	x/m vs p	A curve from the origin that bends over, since 1/n < 1	Yes
   B	log x/m vs log p	A straight line, slope 1/n, intercept log k	Yes
   C	x/m vs c	x/m = k c^(1/n): a curve through the origin, not a straight line with a positive intercept	No
   D	x/m vs p^(1/n)	x/m = k × p^(1/n): a straight line through the origin with slope k	Yes

2. So. Graphs A, B and D all follow from x/m = k p^(1/n). Graph C does not, so the answer is (c).

The idea to keep. For any isotherm graph, put the plotted axes into x/m = k p^(1/n). If the equation becomes y = mx or y = mx + c in those variables, the graph is a straight line. If it does not, the graph is a curve.

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