What role does glycerol play in extending the life of soap bubbles?

• A. It thickens the bubble film to a solid shell.
• B. It alters the color of the bubbles.
• C. It adheres to water molecules, helping to compensate for evaporation.
• D. It neutralizes soap molecules to prevent breakdown.

Answer: (C)

The main idea is that glycerol helps keep the bubble film hydrated and less prone to thinning, which slows its eventual collapse. Soap bubbles are tiny films of soapy water that evaporate over time. Glycerol is a humectant, so it attracts and binds water molecules, slowing the rate at which water leaves the film. That keeps the film thicker for longer and reduces drying that would make it crack.

In addition, glycerol increases the film’s viscosity, which slows the flow of liquid toward the edges and helps the film stay intact instead of draining away too quickly. Its higher boiling point means it doesn’t evaporate away as quickly as water, helping maintain the film’s composition over time.

So, this combination—retaining moisture in the film and thickening it—is what extends the life of soap bubbles.