Question

_____ is almost the pure form of carbon.

Answer 1

DIAMOND and GRAPHITE is the pure form of C-atom.

HOPE IT HELPS YOU

Answer 2

The purest form of carbon is fullerene. It is also called as $\bold{\mathrm{C}_{60}}$. It is one of the allotrope of carbon that is composed of carbon atom only.  

Allotropes are the different forms of same elements which show different physical properties with almost same chemical properties as allotropes are composed of same elements.  

Here fullerenes, diamond, graphite are different forms of carbons hence they are allotropes. Other examples of allotropes are coal, charcoal, etc.