(a) Name the three classes in which elements are classified. Which was the first metal used by man?
(b) Name the metal and non-metal present in abundance in the earth crust.
Name the three categories in which all the elements are classified.
it is said that as per dobereiner`s classification, most elements were in groups of three , that means not all elements classified by him were in groups of three . Give an example in which the group classified by him were not in groups of three.