Diamond and graphite are both composed of which element?

Diamond and graphite are both composed entirely of carbon, which is the reason why choice C is the correct answer. Despite being made of the same element, carbon, these two forms (allotropes) exhibit quite different physical properties due to the variations in their crystal structures. In diamond, carbon atoms are arranged in a tetrahedral structure that creates a strong three-dimensional network, leading to its characteristic hardness and brilliance. In contrast, graphite has layers of carbon atoms arranged in a planar structure where the layers can slide over one another, which accounts for its lubricating properties and softness. The distinction in their structures illustrates the importance of atomic arrangement, even when composed of the same type of element, highlighting the unique behaviors of carbon in different forms.