Question

A non-metal X exists in two different forms Y and Z. Y is hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y and Z.

Answer 1

A non-metai X is carbon (C). Carbon exists in two different forms called the allotropes of carbon. These allotropes are diamond and graphite. 
Y is diamond because diamond is the hardest natural substance. 2 is graphite which is good conductor of electricity.