Solution

Zeta potential is the potential difference between the dispersion medium
and the stationary layer of fluid attached to the dispersed particle so value of zeta potential decrease when opposite charge is adsorbed on surface of colloidal particle.
The higher the zeta potential, the stronger the repulsion, the more stable the system becomes. For instance, high zeta potential of the fat droplets in milk prevents them against coalescence.
Lyophilic colloids are liquid loving colloids (Lyo means solvent and philic means loving).
In Lyophilic sol, forces of interaction between colloidal particles and liquid are quite strong. Hence, Lyophilic sols are very stable and do not precipitate/coagulate easily. However, addition of very large quantities of electrolytes can cause particles to precipitate.