Question

what is atomic mass unit
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Answer 1

An atomic mass unit is defined as a mass equal to one twelfth the mass of an atom of carbon-12. The mass of any isotope of any element is expressed in relation to the carbon-12 standard. For example, one atom of helium-4 has a mass of 4.0026 amu.

Answer 2

Atomic weight is measured in atomic mass units (amu), also called daltons.

See below for a list of chemical elements and their atomic weights.

In atom

 Atomic mass and isotopes. … measured in terms of the atomic mass unit, which is defined to be 

1/12 of the mass of an atom of carbon-12, or 1.660538921 × 10−24 gram.