Question

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

• A. carbon
• B. diamond
• C. graphite
• D. none of the above

Answer 1

Answer: (B)

diamond

A non-metal $X$ is carbon because it exists in two different forms, $Y$ as diamond and $Z$ as graphite. $Y$ that is diamond is the hardest natural substance (diamond cannot conduct electricity, so there are no delocalised electrons and it is very rigid, so ions do not slide over each other), whereas $Z$ which is graphite is a good conductor of electricity (because the carbon electrons in graphite are delocalized. In short terms, the molecular orbitals of the carbon atoms in graphite extend across the planes of carbon due to its symmetry).