For Tyndall effect, the diameter of the dispersed particles is not much smaller than the wavelength of the light used.
So, the correct option is (B): The diameter of the dispersed particles is much smaller than the wavelength of the light used.
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend the definition to include substances like aerosols and gels.
Example of Colloids:
Read More: Classification of Colloids
Colloids contain ionic impurities and other categories of impure substances that decrease the quality of colloids used in various applications. Following are the methods to purify the colloids.