Which of the following is NOT an example of a flocculating agent?

• A. Clays
• B. Electrolytes
• C. Surfactants
• D. Methylcellulose

Answer: (D)

Flocculation involves forming loose, easily redispersible aggregates of particles, typically by reducing interparticle repulsion or creating bridges between particles. Clays help by providing a surface that can bridge between particles, linking them. Electrolytes promote flocculation by screening charges on particle surfaces and compressing the electrical double layer, allowing van der Waals forces to dominate and particles to come together. Surfactants can induce flocculation as well, by adsorbing at interfaces and reducing surface charge or by enabling hydrophobic interactions that bridge particles.

Methylcellulose, instead, is a polymer used as a suspending or thickening agent. It increases the viscosity of the medium and can impart steric stabilization, which slows sedimentation and makes the suspension easier to redisperse, but it does not promote the formation of flocs through bridging or charge neutralization. Therefore, it is not a flocculating agent.