Diamond is the hardest substance on Earth. It is a form of carbon that is made up of carbon atoms that are arranged in a tetrahedral structure. This structure makes diamond very strong and resistant to wear and tear. Diamond is also very dense, which makes it a good conductor of heat and electricity.
Buckminsterfullerene, also known as buckyball, is a spherical molecule made up of 60 carbon atoms arranged in a soccer ball-like structure. Buckyball is a very strong material, but it is not as hard as diamond.
Graphite is a form of carbon that is made up of carbon atoms that are arranged in a hexagonal structure. Graphite is a soft material that is used in pencils and lubricants.
Iron is a metal that is found in the Earth’s crust. Iron is a strong material that is used in construction and manufacturing.
Therefore, the correct answer to the question “Which of following is hardest substance?” is C. Diamond.