Lyophilic sol is more stable than lyophobic sol due to the presence of an envelope of solvent layer (water) around colloidal particles (solvation).
Thus, lyophilic colloids are more soluble than lyophobic colloids.
When lyophilic sol is added to lyophobic sol, lyophilic particles forms a layer around lyophobic particles and protects the latter from electrolytes.
Thus, lyophilic sols used for this purpose are called protective
colloids.
Hence, option (a) is the correct answer.