Question

Atomic numbers of a few elements are given below.
$10,20,7,14$
Identify the correct sequence of the periods to which they belong from the following options.
A.$2,4,2,3$
B.$3,2,3,2$
C.$2,2,3,3$
D.$3,3,2,2$

Answer 1

In order to identify the periods to which an element belongs we must know how many electrons that element has and consequently the electronic configuration can give us an idea about the position of that element in the periodic table.
-The atomic number of an element provides information about the total number of electrons contained by that atom as well as, how many electrons are present in the outermost orbital.

Complete answer:
The horizontal rows in a periodic table are termed as Periods and the vertical columns are termed as Groups. There are $7$ periods and $18$ groups present in the Periodic Table. The atomic number of an element increases as we move down the group as well as, across a period.
So, we can conclude that Carbon has the atomic number $6$, and the element that comes after it is Nitrogen with atomic number $7$ which belongs to period $2$. We know that the element which has atomic number $10$ is a Noble gas called Neon, which lies in the period $2$.
Now we know that the element Calcium has the atomic number $20$ which belongs to the$4$ period.
Lastly, the element under atomic number $14$ is the Silicon, which belongs to the third period.
Hence we can say that, the correct sequence according to the atomic number in the question is $2,4,2,3$
Hence, the correct option is (A).

Note:
-Elements which belong to the same group have the same number of electrons in the outermost shell. in other words when we move down a group, one more orbital gets added to the atom but the number of electrons in the outermost shell remains the same.
-Alternatively, a group of an element can be identified by its outermost shell’s electronic configuration.