Answer
(a) The atomic number is the number of protons in the nucleus of an atom. It identifies that atom as being a member of a specific element.
(b) The mass number is the number of protons and neutrons in the nucleus of an atom.
(c) Isotopes of an element have the same number of protons and electrons but differ in the number of neutrons in the nucleus of the atom. This also means that the mass numbers of the different isotopes will be different.
Work Step by Step
(a) The atomic number is the number of protons in the nucleus of an atom. It identifies that atom as being a member of a specific element.
(b) The mass number is the number of protons and neutrons in the nucleus of an atom. Because an electron has a negligible mass as compared to protons and neutrons, electrons are not used in calculating the mass of an atom.
(c) Isotopes of an element have the same number of protons and electrons but differ in the number of neutrons in the nucleus of the atom. This also means that the mass numbers of the different isotopes will be different. Some isotopes are unstable and can decompose to other substances in a short amount of time.
