The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is termed as adsorption. There are two types of adsorption. In physisorption, attractive forces are mainly Van der Waals while in chemical adsorption adsorbate is held to the adsorbent by chemical bonds. Adsorption increases with increase in pressure and decreases as temperature is increased.
For Freundlich isotherm, graph of \(log(x/m)\) is plotted against \(log P\). The slope of line and its \(Y\) axis intercepts respectively are:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \(\frac{1}{n}, log k\)
The Freundlich adsorption isotherm relates the amount adsorbed per gram of adsorbent to the pressure at constant temperature:
\( \displaystyle \frac{x}{m} = k\,P^{1/n} \quad (n > 1) \)
Taking logarithms:
\( \displaystyle \log\frac{x}{m} = \frac{1}{n}\log P + \log k \)
This is y = mx + c with y = log(x/m) and x = log P. So the straight line has slope = 1/n and intercept on the y-axis = log k.
Why the other options are incorrect
Option (1) \(\frac{1}{n}, k\) — Incorrect. The slope is right, but on a log–log plot the intercept is log k, not k.
Option (3) \(n, 1/k\) — Incorrect. The exponent of P is 1/n, so the slope is 1/n, not n; 1/k appears nowhere in the equation.
Option (4) \(n, \frac{1}{log k}\) — Incorrect. Both the slope and the intercept are inverted.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Adsorption Isotherms – …
