Question

explain the need of term average atomic mass

Answer 1

The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance (the decimal associated with percent of atoms of that element that are of a given isotope). ... An element does not have an absolute atomic mass.

Answer 2

The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance. An element does not have an absolute atomic mass