Question

Atoms of elements in a group on the periodic table have similar chemical properties. This similarity is most closely related to the
A) Atomic numbers
B) Atomic masses
C) Number of principal energy levels
D) Number of valence electrons

Answer 1

According to modern periodic law “The physical and chemical properties of elements are a periodic function of their atomic numbers”.
The general properties of matter such as color, density, hardness, are examples of physical properties. Properties that describe how a substance changes into a completely different substance are called chemical properties. Flammability and corrosion/oxidation resistance are examples of chemical properties.

Complete solution:
If elements are arranged in the order of increasing atomic numbers, elements with similar chemical properties occur at regular intervals
Elements coming after intervals of $2,8,8,18,18{\text{ }}\& {\text{ }}32$ have similar physical and chemical properties occur. They are thus defined as one group.
This is the basic definition of modern periodic law.
Atoms from the same Group of the Periodic Table have the same number and symmetry of valence electrons, and this electronic similarity should give rise to similar chemistry.

**Hence, option “A” is correct

NOTE: **
Properties of elements depend on the way the atoms bond with each other, which depends on the valence electrons. The elements bond to achieve stable electronic configuration, which is octet. Atoms donate, accept and share an electron which depends on the valence electrons. Therefore, atoms with equal number of valence electrons share or bond in a similar way and hence they have similar chemical properties, that is they form hydrides, halides, oxides and several other compounds of similar type.