What is the atomic weight of an element that has two isotopes one with a mass of 30 amu and the other with a mass of 32 amu?

The Atomic Mass of the element cannot be discovered with the given information. It was not specified as to the ratio of the isotopes of the element. If they two isotopes are equally represented, then it's half the sum of the masses of the two isotopes, which is 63 + 65 = 128, and 128 / 2 = 64 amu.

If another ratio (or perhaps a percentage) of the isotopes if given, then a calculation can be made to discover the atomic mass of the element. This calculation will reflect the different amounts of the two isotopes present in samples of that element.

Added:Though the answer given here is correct for the question stated above, there is a more clearing answer for the suggested question: Which element has two isotopes .... (etc.).

This is typically true for copper, Cu, atom no. 29, of which two natural occurring isotopes exist:

• Cu-63, mass 62.92960 a.m.u., occurrence 69.1%
• Cu-65, mass 64.92779 a.m.u., occurrence 30.9%

The average (relative) atomic mass = 63.55