Similarity in chemical properties of the atoms of elements in a group of the Periodic table is most closely related to :
atomic numbers
atomic masses
number of principal energy levels
number of valence electrons
As learnt in
Modern periodic law -
The physical and chemical properties of elements are periodic functions of their atomic number.
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Elements that are in the same group, most of the times, have the same number of valence electrons. The number of valence electrons is directly related to the chemical properties of elements.
Hence, the option number (4) is correct.