(a) The modern periodic table has been evolved through the early attempts of Dobereiner, Newland, and Mendeleev. List one advantage and one limitation of all the three attempts.(b) Name the scientist who first of all showed that atomic number of an element is a more fundamental property than its atomic mass.(c) State Modern periodic law.

	Advantage:	Limitation:
Dobereiner	Dobereiner gave an idea of the classification of elements in the form of triads.	He could not able to arrange all elements present at that time.
Newland	Newland arranged elements in order of increasing atomic mass and encouraged other chemists to correlate the properties of elements with their atomic masses. He said if the element arranges in the increasing order of their mass, the properties of every eight elements were similar to those of the first one.	He could arrange elements only up to calcium.
Mendeleev	Mendeleev periodic table is based on the Mendeleev periodic law which states that the physical and chemical properties of elements are a periodic function of their atomic masses. It means that when the elements are arranged in order of increasing atomic masses, the elements with similar properties recur at regular intervals.	The position of rare earth elements was not clear. They were placed in group IIIA

 (b) In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass.

(c) The Modern periodic law states “The chemical and physical properties of elements are a periodic function of their atomic numbers”.