it is the total number of protons plus the total number of neutrons expressed in Atomic Mass units
Generally the term "atomic mass" is used for isotopes. For elements is preferred now "atomic weight".
No two elements may have the same atomic number. But two elements may have same atomic mass. Hence atomic number is better than atomic mass.
By Atomic Mass
The molar mass of a compound is the sum of atomic weights of the contained elements in the molecule.The expression atomic weight is correct for elements; for isotopes is correct atomic mass.
Gold is a meta element. Atomic Mass of it is 197.
Atomic Mass.
Iron is a metal element. Atomic mass of it is 55.84.
I suppose that you think to atomic weights (not mass) of chemical elements and the molecular mass.
Mendeleev arranged the elements in the periodic table according to their atomic masses.
the 2kg is closest to 2020g because it is the only number that can work for this answer.
Mendeleev arranged elements in order of increasing mass. Later modern periodic table was discovered that contains elements arranged by atomic number.
We can find atomic mass and mass number in chemical elements. Atomic mass is about weight of the atom. Mass number is about total of neutrons and protons.