Which ion has the minimum coagulation value?

Which of the following ions has greater coagulating power for a negatively charged sol?

The protecting power of lyophilic colloidal sol is expressed in terms of

When the dispersion medium in a colloidal system is a gas,it is called ....

Tyndall effect is observed only when:
$(i)$ the diameter of the dispersed particles is not much smaller than the wavelength of the light used.
$(ii)$ the refractive indices of the dispersed phase and the dispersion medium differ greatly in magnitude.
$(iii)$ the size of the particles is generally between $10^{-11} \ m$ and $10^{-9} \ m$ in diameter.
$(iv)$ the dispersed phase and the dispersion medium can be seen separately in the system.

Which one of the following is a hydrophilic colloidal sol?