For preparing a flocculated suspension, all of the following can be added except :

To determine the correct answer regarding what should not be added in the preparation of a flocculated suspension, it's important to consider the properties of flocculation and suspension stability.

1. Understanding Flocculation: Flocculation is a process where fine particulates are agglomerated into a floc. The aim is to enhance the stability of the suspension and prevent complete sedimentation.

2. Common Agents Used in Flocculated Suspensions: Common agents that can be used to promote flocculation include flocculants (such as certain clays, gums, and other polysaccharides), electrolyte salts (which can neutralize charges on particle surfaces), and surfactants.

3. Agents That Should Not Be Used: Typically, substances that would prevent flocculation, such as highly charged surfactants or certain stabilizers that work through steric stabilization (like polyethylene glycol), should not be added. These agents can lead to deflocculation, contradicting the goal of preparing a flocculated suspension.

In conclusion, to correctly answer the question, one must identify the substance that does not contribute to or hinders the flocculation process.