Atomic Number definition: The number of protons within the nucleus of x atom.
Atomic Mass definition: The number of protons and/+ neutrons within the nucleus of x atom.
The given information states that the element has 8 protons and 8 neutrons in its nuclei with 8 electrons revolving around it. If the atomic number is 'the number of protons' and we have 8 given protons, our answer would be 8. If the atomic mass is protons + neutrons and we have 8 protons and neutrons, our answer for atomic mass would inevitably be 16.
Therefore
Atomic number: 8
Atomic mass: 16
answer: 3.40625 moles
Explanation: see the attached pics
57.0 is it rounded to three sig figs. You count three spaces then round from there, which would be the zero and you would round down because the four is there.
