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.
Which of the following is not application of adsorption?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Inversion of cane sugar using mineral acids as catalysts
Adsorption is used wherever a solid surface takes up molecules from a gas or a solution. The inversion of cane sugar is different: the \( \ce{H^{+}} \) ions of the mineral acid are in the same phase as the sucrose solution, so it is homogeneous catalysis, and no surface is involved:
\( \ce{C12H22O11 + H2O} \xrightarrow{\ce{H+}} \ce{C6H12O6 (glucose) + C6H12O6 (fructose)} \)
Option (1) Control of humidity using silica gel — An application of adsorption. Silica gel adsorbs water vapour from the air.
Option (2) Separation of noble gases using charcoal — An application of adsorption. Coconut charcoal adsorbs the noble gases to different extents at different temperatures, which separates them.
Option (3) Removal of colouring matter from solutions — An application of adsorption. Animal charcoal adsorbs the coloured impurities, e.g. in decolourising cane sugar juice.
Option (4) Inversion of cane sugar using mineral acids as catalysts — Not an application of adsorption. It is homogeneous catalysis: the acid and the sugar solution are in one phase.
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):
Applications of Adsorption – …
Homogeneous Catalysis – “When the reactants and the catalyst are in the same phase (i.e., liquid or gas), the process is said to be homogeneous catalysis. … (iii) Hydrolysis of sugar is catalysed by H+ ions furnished by sulphuric acid. … Both the reactants and the catalyst are in the same phase.”