The most stable form of carbon refers to the form that has the strongest chemical bonds and is least likely to undergo a chemical reaction or change.

Option 1: Diamond is a form of carbon in which each carbon atom is bonded to four other carbon atoms in a tetrahedral structure. It has a rigid lattice structure and is known for its hardness. Diamond is indeed a stable form of carbon and is often used in jewelry and cutting tools.

Option 2: Graphite is another form of carbon, but unlike diamond, the carbon atoms in graphite are arranged in layers that can easily slide over each other. This arrangement gives graphite its characteristic softness and ability to conduct electricity. While graphite is stable, it is not as stable as diamond because the carbon bonds in graphite are weaker and more susceptible to reacting with other substances.

Option 3: Fullerene refers to a group of carbon molecules that have a hollow sphere or tube-like structure. Fullerene molecules, such as C60, have a highly stable arrangement of carbon atoms. However, while fullerene is stable, it is not as stable as diamond because the bonds between the carbon atoms in fullerene are weaker.

Option 4: Coal is primarily composed of carbon, as well as other elements such as hydrogen, sulfur,