What defines nanomaterials?

Nanomaterials are specifically defined by their size, particularly with regard to nanoparticles which are typically less than 100 nanometers in one dimension. This size range is significant because it imparts unique physical and chemical properties to materials, influencing reactivity, strength, and other characteristics that differ substantially from bulk materials.

The correct choice articulates that nanomaterials contain nanoparticles smaller than 100 nanometers, which is a fundamental criterion for classifying materials within this category. This size allows for quantum effects and increased surface area-to-volume ratios, which are crucial in various applications, including electronics, medicine, and materials science.

Other choices do not accurately encapsulate this definition. For instance, materials that are less than one meter in length cover a broad range and do not specifically relate to the unique characteristics of nanomaterials. Similarly, stating that substances contain particles larger than 100 nanometers contradicts the common scientific definition, as it excludes materials that fall within the nanometer range. Lastly, compounds with organic matter at a microscopic level lack the specificity of size, thus failing to define nanomaterials accurately based on the established criterion of particle dimensions.