Question

The number of periods present in the long form of the periodic table are:
(A) $17$
(B) $6$
(C) $7$
(D) $13$

Answer 1

Firstly we should be clear what exactly a period is, it is the arrangement of the periodic table which has the elements with the same amount of shells in their natural state or neutral state. Now in the modern form of the periodic table it is observed that there are $18$ columns and $7$ rows i. the complete modern day periodic table.

Complete answer: Firstly we need to know what exactly a period is :
Any period in the modern periodic table refers to as a row of chemical elements with the same ultimate shell. That means that all elements which are in the row must have the same number of electron shells.
It is also observed that all the elements are arranged such that each next element in a period has one more proton and is less metallic than its predecessor. When the elements are arranged in this way, the formed groups of elements in the same column have similar chemical and physical properties. This is the property reflecting the periodic law. As per now, a total of $118$ elements have been discovered by the scientists.
Now as per the modern form of periodic table it is observed that there are a total of the $7$ periods in the long form of table.

Therefore the correct option is option (C), $7$ .

Note: No element of the eighth period has yet been synthesized. A g-block is predicted. It is not clear if all elements predicted for the eighth period are in fact physically possible. There may therefore be no eighth period.