State how carbon occurs in the free state and in the combined state.

Define the term 'allotropy'. Give a reason why carbon exhibits allotropy.

Compare the structure of the crystal of diamond & graphite with special reference to the reason for diamond being the hardest natural substance while graphite one of the softest. Compare the electrical & thermal conductivity of the two crystalline allotropes of carbon.

With reference to the structure of the two crystalline allotropes of carbon, state why diamond is inert or unreactive while graphite is comparably more reactive.