Assertion ( A) : Modern periodic table is known as the long form of the periodic table 

Reason ( R) : Modern periodic table consists of seven groups and eighteen periods 

Modern periodic table is known as the long form of the periodic table because it consists of eighteen groups and seven periods. The modern periodic table is called “long form of periodic table since in comparision to Mendeleev’s periodic table it is longer and have capacity to hold not only accomdate those elements which have been discovered but also which are yet to be discovered.