What are the observable structures at the atomic scale?

The correct choice identifies atoms and molecules as the observable structures at the atomic scale. Atoms, which are the basic units of matter, combine to form molecules, which are groups of two or more atoms bonded together. These structures are fundamental to understanding both chemistry and biology, as they form the building blocks of all substances.

At this atomic scale, scientists can observe characteristics such as atomic size, structure, and interactions with other atoms or molecules through various methods, including microscopy techniques and molecular modeling. Understanding the behavior and properties of atoms and molecules is crucial for explaining chemical reactions, biological processes, and the properties of materials.

In contrast, plants, cells, and countries are not at the atomic scale; they encompass larger and more complex structures. Plants consist of numerous cells, which are made up of various molecules and atoms. Similarly, cells are the basic unit of life but operate at a higher organizational level than individual atoms or molecules. Countries represent sociopolitical structures entirely unrelated to atomic or molecular biology.