WAEC Chemistry 2016 Paper

Concept:Elements form bonds to achieve a stable octet electron configuration.Explanation:Element $_{20}$Y has an electron configuration of $2, 8, 8, 2$, so it has 2 valence electrons.Element $_8$Z has $2, 6$, so it needs 2 electrons to complete its octet.Y readily loses its 2 valence electrons to form a $\mathrm{Y}^{2+}$ ion.Z gains those 2 electrons to form a $\mathrm{Z}^{2-}$ ion.The oppositely charged ions attract, forming an ionic bond.Since one $\mathrm{Y}^{2+}$ ion combines with one $\mathrm{Z}^{2-}$ ion, the formula is YZ.Answer:An ionic compound, YZ is formed.Correct option: C.