Answer
(a) 7 protons, 8 neutrons and 7 electrons.
(b) 27 protons, 33 neutrons and 27 electrons.
(c) 53 protons, 78 neutrons and 53 electrons.
(d) 58 protons, 90 neutrons and 58 electrons.
Work Step by Step
("P" = Number of protons; "$e^-$ = Number of electrons"; "N" = Number of neutrons)
1. Number of protons:
$P = Z$ (Atomic number) (Bottom left number);
(a) 7
(b) 27
(c) 53
(d) 58
2. Number of electrons
$e^- = P$ (because they are neutral)
(a) 7
(b) 27
(c) 53
(d) 58
3. Number of neutrons:
Each proton and neutron is responsible for 1 unit of mass:
$P + N = A$ ("A" is the top left number)
Therefore: $N = A - P$
(a) $N = 15 - 7 = 8$
(b) $N = 60 - 27 = 33$
(c) $N = 131 - 53 = 78$
(d) $N = 148 - 58 = 90$
