Here's why:

* Solubility is based on "like dissolves like" principle: This means substances with similar molecular structures and intermolecular forces are more likely to dissolve in each other.

* Benzene is a nonpolar solvent: It has weak intermolecular forces (Van der Waals forces).

* Polystyrene is a nonpolar polymer: Its long chains are composed of repeating hydrocarbon units, also exhibiting weak Van der Waals forces.

* Polystyrene and benzene are compatible: While they don't truly dissolve, polystyrene can swell in benzene due to the similar nonpolar nature. The benzene molecules can penetrate the polystyrene structure, causing it to expand.

However, it's important to note that:

* This swelling process is not a true dissolution. The polystyrene chains do not break down and form individual molecules in the benzene solution.

* It is not recommended to dissolve polystyrene in benzene due to the potential health hazards associated with benzene.

In summary: While polystyrene and benzene share similar nonpolar characteristics, they don't truly dissolve. Instead, polystyrene swells in benzene due to the compatibility of their nonpolar nature. However, it's important to handle benzene with caution due to its toxicity.