The gold number range of some of the lyophilic colloids is given below:
A: 0.005 - 0.01, B: 0.15 - 0.25, C: 0.04 - 1.0, D: 15 - 25.

Consider a water tank shown in the figure. It has one wall at \(x = L\) and can be taken to be very wide in the z direction. When filled with a liquid of surface tension \(S\) and density \( \rho \), the liquid surface makes angle \( \theta_0 \) (\( \theta_0 < < 1 \)) with the x-axis at \(x = L\). If \(y(x)\) is the height of the surface then the equation for \(y(x)\) is: (take \(g\) as the acceleration due to gravity) 
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.