Polystyrene is widely used as packaging materials for fragile objects during transportation because of its

Analysis of the Question

The question asks for the specific physical property of polystyrene that makes it ideal for packaging fragile items. We need to evaluate the options based on the material's structural characteristics and its function in protecting goods from impact.

Concept Explanation

Polystyrene, especially in its expanded form (often called Styrofoam), is a polymer made from styrene monomers. When manufactured for packaging, it is processed into a foam structure containing many trapped air pockets.

• Density vs. Compressibility: While polystyrene is indeed light and has low density, those properties alone do not explain why it is used for protection.
• The Role of Compressibility: When an object is wrapped in a material, the goal is to absorb kinetic energy during a collision or drop. A material that is highly compressible can deform under pressure, effectively increasing the time over which the impact force is applied to the fragile object. This reduces the impulse (force) experienced by the object, preventing it from breaking.

Step-by-Step Solution

1. Evaluate A and B: Polystyrene is light and has low density, which makes shipping cheaper, but these properties do not provide shock absorption.
2. Evaluate C: High density would make the material hard and rigid, which would likely transmit impact forces directly to the fragile object rather than absorbing them.
3. Evaluate D: Because of its foam structure, polystyrene is highly compressible. When a force is applied (like a drop), the air pockets collapse, absorbing the energy of the impact. This cushioning effect is the primary reason it is used for packaging.

Conclusion

While polystyrene is light (low density), its ability to compress and absorb mechanical shock is the functional reason it is used to protect fragile items.

Exam Tip

When you see questions about packaging materials in Chemistry or Physics, look for terms related to energy absorption or cushioning. Materials that are "compressible" or "elastic" are usually the correct answers for shock protection, whereas "dense" or "hard" materials are used for structural support.