What is a common characteristic of nanoparticles?

Nanoparticles exhibit a common characteristic of being typically active in chemical reactions due to their high surface area to volume ratio and unique physical and chemical properties. This increased surface area allows nanoparticles to interact more effectively with other materials, enhancing their reactivity compared to bulk materials. For instance, nanoparticles can serve as catalysts in various chemical reactions, promoting efficiency and reaction rates. Additionally, their small size often enables them to penetrate biological barriers, making them particularly useful in various applications such as drug delivery and environmental remediation.

The other options represent misconceptions about nanoparticles. They are not visible to the naked eye, as they are typically on the nanoscale (1 to 100 nanometers). They can be smaller than 100 nanometers, hence the characterization of nanoparticles does not require them to be larger than this size. Lastly, nanoparticles can be composed of solids, liquids, or even gases, making the assertion that they are only solid materials incorrect.