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

Many metals and non-metals exist in more than one form and show allotropism. It is the property of some chemical elements in which the elements exist in two different forms in the same physical state and those forms are known as the allotropes of the elements.

Complete step by step answer:
Now we will start with our question: the question says that a non-metal $X$ exists in two different forms $Y$ and $Z$. So, we can conclude from the property of allotropes that $Y$ and $Z$ are allotropes of a non-metal $X$. Now concerning this context, we will use the given properties of $Y$ and $Z$ predict all the three elements $X,Y$ and $Z$. Now according to the question, $X$ is a non-metal with two allotropes $Y$ and $Z$. Now $Y$ is the hardest natural substance and we know that the hardest natural substance that exists is diamond. Now when we consider the property of $Z$ which is given as it is a good conductor of electricity and when we relate it with $Y$ we can conclude that $Z$ is graphite which is a good conductor of electricity.
Now everything is clear to us that $Y,Z$ are diamond and graphite respectively and we know that carbon is the only non-metal which exists in two different forms diamond and graphite. So, we can conclude that $X \to carbon,Y \to diamond,Z \to graphite$.
Therefore, the correct option is (B).

Note:
Diamond, graphite, and fullerenes are the three allotropes of carbon. In all the three allotropes the carbon atoms are joined by covalent bonds. But these allotropes differ from each other due to different physical arrangements and chemical behaviour.