Question

Which of the following is not an allotrope of carbon?
(A) Graphite
(B) Granite
(C) Diamond
(D) Fullerene

Answer 1

Hint: Allotropy is defined as the existence of a chemical element in two or more forms that have different arrangements of atoms in crystalline solids or that contain different no. of atoms. Granite is a light-colored rock which consists of coarse grains of quartz, potassium feldspar, and sodium feldspar.

Complete answer step by step: There are several allotropes of carbon. These are diamond, graphite, fullerenes - ${C}_{60}$, ${C}_{540}$, and ${C}_{70}$, amorphous carbon, and single-walled carbon nanotube, or buckytube. But the most common allotropes of carbon are diamond, graphite, and ${C}_{60}$.
Let us now discuss them one by one.
(i) Diamond: It is probably the most common known allotrope of carbon. The carbon atoms in diamond are arranged in a variation of the face-centered cubic crystal structural lattice. Each carbon atom is covalently bonded in a tetrahedron to the other four carbon atoms. Dye to this stable network, diamond is the hardest material.
(ii) Graphite: It is another allotrope of carbon that is present in its purest form. Unlike diamond, graphite is an electric conductor and a semi-metal. It has a layered, planar structure in which each layer has carbon atoms arranged in a hexagonal lattice. It can conduct electricity because the electrons are arranged in such a manner that they are allowed to move freely through the planes of the layers. It displays extraordinary electrical, thermal, and physical properties.
(iii) ${C}_{60}$: It is commonly known as Buckminsterfullerene or buckyballs. These are molecules composed entirely of carbon and take on the shape of hollow spheres. It is in a shape that is the same as the shape of a football but way smaller in size. They used nanotechnology to combine the carbon atoms in this way. They are used in tackling melanoma and other tough cancers.
 Therefore, to answer the question, granite is not an allotrope of carbon. Hence, option (b) is the correct answer.

Note: Students tend to confuse between graphite and granite. Note that these two are totally different in every aspect. Graphite is purely made up of carbon and is black in color, whereas granite is made of coarse grains of quartz, potassium feldspar, and sodium feldspar and is a light coloured plutonic rock.