Question

What is the purest form of carbon?

a) fullerene

b) carbon black

c) diamond

d) coke

e) any other

Answer 1

Diamond is widely accepted the as purest form of carbon. So, if only one option is correct, you should go for option (C) Diamond

In case multiple correct answers are there, Then purest forms of Carbon are Diamond and Graphite..
Both of them have similar chemical properties , however the differences in physical properties give rise to different structures . A recent pure form of Carbon , called Buckminster fullerene has been discovered recently.
So, there could be 3 possible answers at maximum,
1) Diamond
2) Graphite
3) Fullerene