WAEC Chemistry 2011 Paper

Concept:Transition metal ions often form coloured aqueous solutions because they have partially filled $d$-orbitals.Explanation:Calcium, magnesium, and sodium are $s$-block metals.Their ions, such as $\mathrm{Ca}^{2+}$, $\mathrm{Mg}^{2+}$, and $\mathrm{Na}^{+}$, are colourless in water.Iron is a transition metal.Its ions, $\mathrm{Fe}^{2+}$ and $\mathrm{Fe}^{3+}$, have partially filled $d$-orbitals.These $d$-orbitals absorb visible light to cause electron transitions, producing a coloured solution.Hence, among the given elements, iron is the one that gives coloured ions in aqueous solution.Answer:Iron (Option B)