A colloid is a heterogeneous system in which one substance is dispersed as very fine particles in another substance. Their range of diameters is between 1-1000 nm. Based on dispersed phase and dispersion medium, colloids may be of different types like sol, gel, emulsion, aerosol, foam etc. Based on nature of interaction between two phases, sols are divided into Lyophilic and Lyophobic sols. Colloidal solutions exhibit various properties like Tyndall effect, Brownian movement and Electrophoresis. Stability of colloids is due to presence of charge. If somehow charge is removed, the particles will coagulate. Coagulation rate by various solutions containing ions, is decided by Hardy-Schulze rule. Everyday we come across many colloids. The meals we eat, clothes we wear, wooden furniture etc. are largely composed of colloids.
The range of diameters for colloidal particle is :
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(10^{-9}\) to \(10^{-6}\)m
A colloid lies between a true solution (particles below about 1 nm) and a suspension (particles above about 1000 nm). Colloidal particles have diameters between 1 and 1000 nm. With 1 nm = 10−9 m:
\( \displaystyle 1\ \text{nm} = 10^{-9}\ \text{m},\qquad 1000\ \text{nm} = 10^{3} \times 10^{-9}\ \text{m} = 10^{-6}\ \text{m} \)
So the range is 10−9 to 10−6 m.
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):
Colloids – “… The essential difference between a solution and a colloid is that of particle size. While in a solution, the constituent particles are ions or small molecules, in a colloid, the dispersed phase may consist of particles of a single macromolecule (such as protein or synthetic polymer) or an aggregate of many atoms, ions or molecules. Colloidal particles are larger than simple molecules but small enough to remain suspended. Their range of diameters is between 1 and 1000 nm (10−9 to 10−6 m).”