Method by which lyophobic sol can be protected.

1.  By addition of oppositely charged sol.

2.  By addition of an electrolyte.

3.  By addition of lyophilic sol.

4.  By boiling.

NEETprep Answer: 
 
(3) HINT: Lyophilic sol can protect lyophobic sol.
 
Explanation: Lyophobic sol can be protected by addition of lyophilic sol. As lyophobic sols are readily precipitated on addition of small amount of electrolytes or shaking, or heating hence they are made stable by adding lyophillic sol which stabilises the lyophobic sols.