JAMB Chemistry 2011 Paper

Concept:Hardness of water is caused by dissolved calcium and magnesium salts in the water.Explanation:Hard water contains compounds that release $Ca^{2+}$ and $Mg^{2+}$ ions.Temporary hardness is due to bicarbonates such as $Ca(HCO_3)_2$ and $Mg(HCO_3)_2$.Permanent hardness is due to sulfates and chlorides such as $CaSO_4$ and $MgCl_2$.Among the options, calcium trioxocarbonate(IV), $CaCO_3$, and calcium tetraoxosulphate(VI), $CaSO_4$, are calcium salts that can release hardness-causing ions in water.Sodium salts and metal hydroxides listed in other options do not cause hardness of water.Answer:B. calcium trioxocarbonate (IV) or calcium tetraoxosulphate (VI)