Question

​Justify the numbering of groups from 1 to 18 in the IUPAC long form periodic table.

Answer 1

The elements have been classified in the periodic table into 18 groups.There is a similarity in the properties of the elements (when arranged in their increasing order of masses) after a certain interval.This is known as periodicity.Hence the elements with similar chemical properties and physical properties have been grouped togetjer ,resulting in 18 groups of the periodic table. 
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Answer 2

Answer:

The no. of group in the form of the periodic table is 18 , because it completes its outer most shell. so, there electrons can't be share by this group 18 is in the long from of the peroid table .

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