Question

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.

Answer 1

Dobereiner, gave only three triads which consisted of elements: Lithium , sodium, potassium; calcium, stroncium, barium; chlorine, bromine, iodine.

Other elements such nitrogen, phosphorus; oxygen, sulphur were not classified as triads.