JAMB - Chemistry (2004 - No. 14)
Hardness of water is caused by the presence of ions of
magnesium and silver
calcium and magnesium
sodium and potassium
calcium and sodium
Explication
Water hardness is caused by the presence of positively charged metallic ions, most commonly calcium and magnesium.
Water becomes hard when it comes into contact with limestone and other rocks that contain calcium compounds. For example, rainwater that flows over rocks on its way to a reservoir can pick up calcium and magnesium ions.