Answer : The correct option is, Number
Explanation :
The periodic table is a type of table in which the element are systematically arranged on the basis of the atomic number.
The periodic table have the groups and periods. In the periodic table, there are 7 horizontal rows of elements are known as period and 18 vertical columns of elements are known as group.
Hence, 1A, 3B, and 7A are examples of group number on the periodic table.