How does ozone react with the following?
A. \[\text{PbS }\]
B. \[\text{moist KI }\]
C. \[\text{Hg }\]
D. \[{{\text{C}}_{2}}{{\text{H}}_{4}}\text{ }\]

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Hint: Ozone is an oxidizing agent. It oxidizes another compound. Gain of oxygen or removal of hydrogen is known as oxidation.

Complete step by step answer:
(i) Ozone oxidizes lead sulfide to lead sulphate. Lead sulfide has black color whereas lead sulphate has white color. The byproduct of the reaction is dioxygen.
Write the chemical reaction:
\[\text{PbS + }{{\text{O}}_{3}}\text{ }\to \text{ PbS}{{\text{O}}_{4}}\text{ + }{{\text{O}}_{2}}\]
In the above equation, lead atoms and sulfur atoms are already balanced. To balance the above reaction, add coefficient 4 to ozone and oxygen.
\[\text{PbS + 4 }{{\text{O}}_{3}}\text{ }\to \text{ PbS}{{\text{O}}_{4}}\text{ + 4 }{{\text{O}}_{2}}\]
(ii) Ozone oxidizes moist potassium iodide to iodine. Potassium hydroxide and oxygen are the other byproducts of this reaction.
Write unbalanced chemical equation:
\[\text{KI + }{{\text{H}}_{2}}\text{O + }{{\text{O}}_{3}}\text{ }\to \text{ KOH + }{{\text{I}}_{2}}\text{ + }{{\text{O}}_{2}}\]
Balance iodine atoms by adding 2 to potassium iodide.
\[\text{2KI + }{{\text{H}}_{2}}\text{O + }{{\text{O}}_{3}}\text{ }\to \text{ KOH + }{{\text{I}}_{2}}\text{ + }{{\text{O}}_{2}}\]
Balance potassium atoms by adding 2 to potassium hydroxide.
\[\text{2 KI + }{{\text{H}}_{2}}\text{O + }{{\text{O}}_{3}}\text{ }\to \text{ 2 KOH + }{{\text{I}}_{2}}\text{ + }{{\text{O}}_{2}}\]
This is the balanced chemical equation.

(iii) Ozone oxidizes mercury to mercurous oxide. Mercury meniscus is lost and mercurous oxide sticks to glass. This is called tailing of mercury. To restore mercury meniscus, it is shaken with water.
Write an unbalanced chemical equation.
\[\text{Hg + }{{\text{O}}_{3}}\text{ }\to \text{ H}{{\text{g}}_{2}}\text{O + }{{\text{O}}_{2}}\]
Oxygen atoms are already balanced. Balance mercury atoms by adding coefficient 2 to mercury on the reactants side.
\[\text{2 Hg + }{{\text{O}}_{3}}\text{ }\to \text{ H}{{\text{g}}_{2}}\text{O + }{{\text{O}}_{2}}\]
This is a balanced chemical equation.
(iv) The reaction of ethylene with ozone gives an ozonide. On decomposition of ozonide with zinc dust and water, formaldehyde is obtained.
Write a balanced chemical equation.
\[\text{C}{{\text{H}}_{2}}=\text{C}{{\text{H}}_{2}}\text{ + }{{\text{O}}_{3}}\text{ }\to \text{ 2 C}{{\text{H}}_{2}}\text{O + }{{\text{H}}_{2}}{{\text{O}}_{2}}\]
Each carbon atom of ethylene is oxidized to formaldehyde. Thus, one ethylene molecule gives two molecules of formaldehyde.

Note:
Ozone oxidises other compounds by giving an oxygen atom. Ozone itself gets reduced to a dioxygen molecule by giving an oxygen atom.