(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.
State Modern periodic law.

Explanation

(a) Dobereiner's Triads
Advantage : It was the first genuine scientific attempt to group elements with similar characteristics in traids.
Limitation : The number of triads was limited to a few elements only. Therefore, this attempt could not gam importance.
Newland's Law of Octaves
Advantage : This law for the first time gave the idea of groups. Moreover, the elements were arranged in increasing order of atomic masses.
Limitation : This classification was successful only upto calcium.
Mendeleev's Classification
Advantage : Mendeleev's classification laid che foundation of the Modern Periodic Table. He was successful. in arranging large number of known elements into groups and periods
Limitation : The basis of classification as given by Mendeleev's periodic law was not correct. This led to many limitations e.g. position of hydrogen, position of isotopes etc.
(a) It was given by Moseley in the form of Modern Periodic Law.
(c) According to Modern Periodic Law 'physical and chemical properties of elements are the periodic function of their atomic numbers.