WAEC Chemistry 2021 Paper

Concept:Isotopes of an element have identical atomic numbers but different mass numbers.The atomic number is always fixed for a given element.Explanation:In the standard nuclear symbol ${}^{A}_{Z}\mathrm{X}$, the top number $A$ is the mass number and the bottom number $Z$ is the atomic number.For the neon isotopes given, the top numbers are $20$, $21$, and $22$, so these are the mass numbers.The bottom numbers are $x$, $y$, and $z$, so these must represent the atomic number of neon.Neon has atomic number $10$, meaning every neon atom contains $10$ protons.Changing the number of neutrons produces different isotopes, but it never changes the number of protons or the atomic number.Therefore, all three isotopes must have the same atomic number: $x = y = z = 10$.This relationship is given by option C.Answer:$C.\; x = y = z$