The basis for modern Periodic Table is _____.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Atomic Number
The modern periodic law says that the properties of the elements are a periodic function of their atomic numbers. Henry Moseley showed in 1913 that the atomic number (the number of protons in the nucleus) is the basic property of an element, and the modern periodic table arranges the elements in order of increasing atomic number.
Why the other options are incorrect
Option (1) Atomic Mass — Incorrect. It was the basis of Mendeleev’s periodic table (1869), which left some elements in the wrong order.
Option (2) Physical Property — Incorrect. Physical properties repeat because of the arrangement by atomic number; they are not its basis.
Option (3) Atomic Weight — Incorrect. It is the older name for atomic mass, the basis of Mendeleev’s table.