Question

The atomic mass of an element is

A.The average mass of all the isotopes of the element
B. A measure of the density of that element
C.The mass of the most common isotope of that element
D.The number of protons and electrons in the atoms of the element

Answer 1

It is A. If you actually take the masses of an individual proton, neutron, and electron and calculate the expected mass for the most common isotope, you will see that it differs from the value presented on the period table.