Read the passage below and answer the question:
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 with chemical bonds adsorbent. Adsorption increases with increase in pressure and decreases as temperature is increased.
Which of the following is not application of adsorption?

1. A Control of humidity using silica gel
2. B Separation of noble gases using charcoal
3. C Removal of colouring matter from solutions
4. D Inversion of cane sugar using mineral acids as catalysts