A colloid is a heterogeneous system in which one substance is dispersed as very fine particles in another substance called dispersion medium. Colloids are classified on the basis of physical state of dispersed phase and dispersion medium, nature of interaction between dispersed phase and dispersion medium and types of particles of dispersed phase. There are various methods for the preparation of colloidal solutions such as chemical methods, electrical disintegration and peptization. Colloidal solutions when prepared, generally contain excessive amount of electrolytes, and some other soluble impurities. The process used for reducing the amount of impurities to a requisite minimum is known as purification of colloidal solution. Purification of colloidal solution is carried out by various methods such as Dialysis, Electrodialysis, Ultrafiltration etc. Colligative properties, Tyndall effect, colour, Brownian movement, charge on colloidal particles, electrophoresis, coagulation are various properties exhibited by colloidal solution.
The chemical composition of collodion is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 4% solution of nitrocellulose in a mixture of alcohol and ether.
In ultrafiltration, colloidal particles are separated from the dispersion medium by filter papers whose pores are made small enough to stop them. The pores of ordinary filter paper are reduced by soaking it in collodion, which is a 4% solution of nitrocellulose in a mixture of alcohol and ether, then hardening it with formaldehyde and drying.
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):
Purification of Colloidal Solutions – “… (iii) Ultrafiltration: Ultrafiltration is the process of separating the colloidal particles from the solvent and soluble solutes present in the colloidal solution by specially prepared filters, which are permeable to all substances except the colloidal particles. Colloidal particles can pass through ordinary filter paper because the pores are too large. However, the pores of filter paper can be reduced in size by impregnating with colloidion solution to stop the flow of colloidal particles. The usual colloidion is a 4% solution of nitro-cellulose in a mixture of alcohol and ether.”