Question

The elements A,B,C,D and E have atomic numbers 9,11,17,12 and 13 respectively.Which pair of elements belongs to the same group?
A. A and B
B. B and D
C. A and C
D. D and E

Answer 1

Hint: We know that the valence shell electrons of elements which belong to a same group are the same. So here we will write the electronic configuration of the given elements , and then compare their valencies .The elements which will have the same valence electrons will belong to the same group.

Complete step by step answer:
First of all let us write the electronic configuration of the given elements A , B, C , D and E.
Atomic number of A=9 ;electronic configuration =2,7
Atomic number of B=11 ;electronic configuration=2,8,1
Atomic number of C=17 ;electronic configuration=2,8,7
Atomic number of D=12 ;electronic configuration=2,8,2
Atomic number of E=13 ;electronic configuration=2,8,3
Now comparing the valence electrons of the given elements A, B, C, D and E we clearly notice that the valence electrons of the elements A and C are the same , which means they belong to the same group.The element s and A and B are Fluorine and Chlorine respectively and they do belong to the same group in the periodic table.
So, the correct answer is “Option C”.

Note: A group is known as the column of elements in the periodic table. The chemical properties of the atoms of elements in a group of the periodic table is most closely related to the number of valence electrons. All the chemical properties can be justified just by the number of valence electrons.There are three systems of group numbering for the groups; the same number may be assigned to different groups depending on the system being used. The modern numbering system of "group 1" to "group 18" has been recommended by the International Union of Pure and Applied Chemistry (IUPAC) since about 1990.