Freshly prepared precipitate sometimes gets converted to colloidal solution by ......

1.  Coagulation

2.  Electrolysis

3.  Diffusion

4.  Peptisation

 
 
 
HINT: Peptisation
 
Explanation: Freshly prepared precipitate sometimes gets converted to colloidal solution by peptisation. Peptisation is a process in which by addition of a suitable peptising agent precipitate gets converted into colloidal solution.