WAEC Chemistry 2015 Paper

Concept:A cation forms when an atom loses electrons, but its proton count stays equal to the atomic number.Explanation:The symbol $\mathrm{Z}^{2+}$ shows a charge of $+2$.A $+2$ charge means the atom has lost two electrons.The given ion contains 18 electrons.To find the original electron count, add the lost electrons: $18 + 2 = 20$.In an uncharged atom, protons equal electrons.Thus, the neutral atom has 20 protons.Ion formation does not change the number of protons.So $\mathrm{Z}^{2+}$ must also have 20 protons.Answer:Protons in $\mathrm{Z}^{2+}$ = 20.Correct option: A. 20.