describe, and write equations for, the reactions of the elements with oxygen (to give Na₂O, MgO, Al₂O₃, P₄O₁₀, SO₂), chlorine (to give NaCl, MgCl₂, AlCl₃, SiCl₄, PCl₆) and water (Na and Mg only)

explain, including by use of an equation, the use of chlorine in water purification to include the production of the active species HOCI and CIO\(^-\) which kill bacteria