Which one shows anisotropic behavior?

Explanation

This is the option marked correct in the official UHS answer key. Graphite is crystalline with a strongly layered structure, so properties such as electrical conductivity differ enormously along the layers compared with across them, which is the essence of anisotropy. Coke is amorphous and therefore isotropic. Note that gemstones are crystalline and anisotropic too, and wood is anisotropic in the everyday sense of grain, so this question rests on the crystalline definition.