Question

What determines the atomic mass of an element?

A.
the sum of the protons and the neutrons

B.
the sum of the neutrons and the electrons

C.
the sum of the protons and electrons

D.
the sum of the ions and isotopes

Answer 1

The atomic mass is the mass of the nucleus.

Answer 2

that is clearly answer A.

Answer 3

nature

Answer 4

i read about the policy of openstudy, we should not just give answers, but help, and i did just give answers many times before, i was wrong.

Answer 5

What determines the atomic mass of an element?


it is convention to say that electrons have small mass, about 1/2000 of the mass of a proton. A neutron has a mass comparable to a proton.
If b were the answer, it would not count the mass of the protons, and thus for example the hydrogen atom, having only one proton, no neutrons and one electron, would have the mass of one electron. But Mass spectrometers show another value.
same problem for answer C: it does not count the mass of the neutrons. If C were the answer, there would not be any isotopes of all the elements, but again, there do exist in nature isotopes. Isotopes are elements with same amount of electrons and protons, but they differ in the amount of neutrons, and therefore we can separate isotopes with methods like centrifuges, and other methods i don't know.
If D were the answer , the atomic mass of an isotope is determined by the sum of the ions and isotopes, i would quit science, because the answer doesn't seem to make sense. What do they mean by the ions? All the ions an element can form? And how can one sum ions? Ions are not numbers or variables one can sum up.
Same for isotopes, one can not sum isotopes.
So i personally find answer D not elaborate enough to be comprehensible.
So by elimination of answer b,c, and d, i conclude the one that is left, A