What is graphene?

Graphene is indeed a carbon structure that is one atom thick, which makes it a two-dimensional material. It consists of a single layer of carbon atoms arranged in a honeycomb lattice. This unique arrangement gives graphene extraordinary properties, such as exceptional electrical conductivity, strength, and flexibility. These characteristics arise from the way carbon atoms bond in this single layer format, allowing electrons to move freely across its surface.

In contrast, the other options describe materials that do not accurately represent graphene. A liquid form of carbon does not exist as carbon typically forms solid allotropes under standard conditions. A 3D structure of silicon and oxygen describes a different set of materials altogether, primarily silicates or silicon-based compounds, while a solid form of diamond refers to a crystal structure of carbon in a tetrahedral arrangement, which is entirely different from the two-dimensional structure of graphene. Thus, the definition as a one-atom-thick carbon structure precisely captures what makes graphene unique.