Write the symbol for the atom or ion of the species that contains
(a) 23 protons, 28 neutrons, and 20 electrons.
(b) 53 protons, 74 neutrons, and 54 electrons.
(c) 44 protons, 58 neutrons, and 41 electrons.
(d) 15 protons, 16 neutrons, and 15 electrons.