JAMB Chemistry 2018 Paper

Concept:Electrovalency involves the transfer of electrons from a metal to a non-metal, which changes the metal’s oxidation number.Explanation:In electrovalent bonding, a metal atom loses one or more electrons to achieve a stable electronic configuration.When electrons are lost, the metal atom becomes a positively charged ion, or cation.For example, sodium loses one electron: $\mathrm{Na} \rightarrow \mathrm{Na}^{+} + e^{-}$.The oxidation number of sodium increases from $0$ in the atom to $+1$ in the ion.Similarly, magnesium loses two electrons: $\mathrm{Mg} \rightarrow \mathrm{Mg}^{2+} + 2e^{-}$, so its oxidation number increases from $0$ to $+2$.Therefore, in electrovalency, the oxidation number of the participating metal always increases because it donates electrons.Answer:The correct option is B. increasing.