Question

define the atomic mass

Answer 1

The mass of an atom of a chemical element is expressed in atomic mass unit
it is approximately equal to the sum of protons and neutrons of the atom....

Answer 2

The smallest portion of matter is atom. It is so small in size that it may not be possible to isolate a single atom and then weigh it. Moreover, the mass of the atom of an element is also extremely small. For example, an atom of hydrogen has mass equal to 1. 67×10^-24 g or 1. 67× 10^-27 kg.