Which of the following is an allotropic form of carbon?

Correct option is D

The correct answer is (d) Diamond.
· Diamond is an allotropic form of carbon. Allotropes are different structural forms of the same element, and carbon has several allotropes, including diamond, graphite, and graphene.
· In a diamond, carbon atoms are arranged in a tetrahedral lattice structure, making it one of the hardest known materials. This crystalline arrangement gives diamond its strength and unique properties, such as its brilliance and ability to refract light.
Explanation of Other Options:
· Gypsum: This is a mineral composed of calcium sulfate dihydrate (CaSO₄·2H₂O), not an allotrope of carbon.
· Chalk: Chalk is made primarily of calcium carbonate (CaCO₃), not carbon in its pure form.
· Marble: Marble is a metamorphic rock also primarily composed of calcium carbonate (CaCO₃), not carbon.