Question

Which of the following sequences contains an atomic number of only representative elements?
A. 55,12,48,53
B. 13,33,54,80
C. 3,33,53,87
D. 22,33,55,66

Answer 1

Representative elements are the elements which lie in the group 1 and 2 on the far left and the last six columns or groups on the far right corner of the periodic table.

Complete step by step answer:
The elements from the ‘s’,’p’ groups except the ‘d’ group elements are known as representative elements. Their outer shells are not completely filled with electrons and the elements of this group get the nearest inert gas configuration by losing ,gaining or sharing of electrons. They are chemically active in nature. The periodic group table is divided into two categories: representative elements and the transitional metals.

Elements in which all the inner shells are complete but the outer shell is incomplete is known as representative elements. It means that the elements which have less than 6 electrons in their ‘P’ shell and less than 2 in their ‘s’ shell or their outermost shell are called as representative elements.
In the aforementioned example while doing the electronic configuration of the elements we get to see that for atomic number $3,33,53,87$ contains the sequence in which their outermost shell is incompletely filled
- For atomic number ‘3’ it is $1{s^2}2{s^1}$
- For ‘33’ it is $1{s^2},2{s^2},2{p^6},3{s^2},3{p^6},4{s^2},3{d^{10}},4{p^3}$
- Similarly for ‘53’ $1{s^2},2{s^2},2{p^6},3{s^2},3{p^6},4{s^2},3{d^{10}},4{p^6},5{s^2},4{d^{10}},5{p^5}$ and
- For ‘87’ it is $1{s^2},2{s^2},2{p^6},3{s^2},3{p^6},4{s^2},3{d^{10}},4{p^6},5{s^2},4{d^{10}},5{p^6},4{f^{14}},5{d^{10}},6{s^2},6{p^6},7{s^1}$ which means that all the elements have their outermost shell half filled.

**Therefore the correct option for the representative element sequence is option (C).

Note:**
First two and last six groups of periodic table together are representative elements. Transition metals are the elements in the middle of periodic table.