Q.Define Modern Periodic law.

The Modern Periodic Law replaced Mendeleev's atomic-mass basis with atomic number as the fundamental property that governs periodicity. …

The question asks us to state the Modern Periodic Law.

The Modern Periodic Law, based on the work of Henry Moseley (who showed atomic number, not atomic mass, is the fundamental property of an element), states:

"The physical and chemical properties of the elements are periodic functions of their atomic numbers." …