An atom has 10 electrons, 12 neutrons, and no net charge. What element is this atom, and what are its atomic number and mass?

Since the element is neutral, it has 10 fundamental positive charges, 10 protons, in its nucleus.

In the nucleus, there are also 12 massive, neutral particles, 12 neutrons. The number of protons, Z, defines the atomic number, and the periodic table is arranged according to Z.