Question

In which year, Henry Moseley show that the atomic number is a most fundamental property?
A ) 1910
B ) 1911
C ) 1912
D ) 1913

Answer 1

Hint: First the elements were arranged in according to their increasing atomic masses but according to the Modern periodic law, the properties of elements are the periodic function of their atomic number.

Complete answer:
Before Moseley, the classification of the elements in the periodic table was based on the atomic mass of the elements. The elements were arranged in the increasing order of atomic mass. It was observed that when the elements are arranged in the increasing order of atomic masses, some periodicity in the properties are observed. However several anomalies were observed to this trend.
In 1913, Henry Moseley showed that the atomic number is a most fundamental property.
After this discovery, the classification of the elements in the periodic table was based on the atomic number of the elements. The elements were arranged in the increasing order of atomic numbers. This change of basis of classification from atomic number to mass number resulted in the resolution of several defects in Mendeleev’s periodic table.

Hence, the correct option will be the option D ) 1913.

Note: Atomic mass is the sum of masses of all the protons and neutrons (and electrons) present in the atom. Atomic number gives the number of protons present in the atom.