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

• A. Carboxymethylcellulose
• B. Methylcellulose
• C. Ethanol
• D. Polyvinyl pyrrolidone

Answer: (C)

Suspending agents are substances that increase the viscosity or form a network in the liquid vehicle to keep solid particles from settling quickly. Carboxymethylcellulose and methylcellulose are classic thickening agents that raise viscosity, helping to suspend particles. Polyvinylpyrrolidone also acts as a stabilizer that can enhance suspension stability by increasing viscosity and forming a supportive matrix around particles. Ethanol, on the other hand, is a volatile solvent used to dissolve components rather than to thicken the vehicle or trap particles. It does not provide the rheological properties needed to prevent sedimentation, so it is not used as a suspending agent.