Question

Both coal and diamond are made from the element carbon. Then, why is coal black and easily breakable and diamond white and hard and strong?

Answer 1

Both  coal and diamond have same chemical properties but their physical properties are not similar.The difference lies in the manner in which the carbon atoms are bonded to one another.
In diamond each carbon atom is bonded to three other carbon atoms forming three dimensional structure. In coal, each carbon atom is bonded to three other carbon atoms on the same plane.