(N/A) Atomic number $(Z)$ is defined as the number of protons present in the nucleus of an atom.
The Modern Periodic Law states that the physical and chemical properties of elements are a periodic function of their atomic numbers.
Key aspects of the Modern Periodic Table:
$(i)$ It is based on the electronic configuration of elements,which determines their chemical reactivity and valency.
$(ii)$ It consists of $18$ vertical columns known as groups and $7$ horizontal rows known as periods.
$(iii)$ Elements with similar valence shell electronic configurations are placed in the same group,exhibiting similar chemical properties.