Question

what is meant by a groups of periodic tablel

Answer 1

Groups in the modern periodic tables are the vertical columns. There are 18 groups in the modern periodic table. But there were only 8 groups in the Mendeleev's periodic table.

Answer 2

Mendeleev's periodic table is also known as modern preodic table vertical columns are groups and horizontal are periods .... periods are 7 and groups are 18