Question 3
Why does graphite behave as a lubricant?
The right answer is the one marked above.
The bonds between its layers are weak, so the layers slide. Within each layer the covalent bonds are strong, but the leftover electrons form only weak attractions between one layer and the next.
The carbon atoms are firmly bonded — three to each atom within a layer. Graphite is a giant lattice, not small molecules, and the covalent bonds inside a layer are not weaker than diamond bonds; it is the attraction between layers that is weak.