Which of the following is not a crystalline allotropic form of carbon?
Allotropy is the phenomenon by which the same element can exists in different physical forms. The crystalline allotropes of carbon are diamond, graphite and buckminsterfullerene. They are all made from carbon arranged in different ways. Coal is not an crystalline allotropic form of carbon as it is a mixture of various carbon compounds and other substances. So, it is an amorphous form of carbon.