Question

$S{{O}_{2}}$ gas is used as a bleaching agent. Its bleaching action is------.
A.Temporary and due to its oxidizing nature
B.Temporary and due to its reducing action
C.Permanent and due to its oxidizing action
D.Permanent and due to its reducing action

Answer 1

Bleach is the general name for any chemical reagent which is used in industries and for domestic purpose to get rid of color from a fabric or to remove stains or dyes through a process called bleaching. Examples for bleaching agents are chlorine, alkaline solution of sodium hypochlorite etc.

Complete answer:
Both Sulphur dioxide ($S{{O}_{2}}$) and Chlorine ($C{{l}_{2}}$) act as good bleaching agents.
Bleaching property of chlorine is due to oxidation whereas the bleaching property of sulphur dioxide is due to reduction.
Chlorine reacts with water and produces nascent oxygen.
$C{{l}_{2}}+{{H}_{2}}O\to [O]+2HCl$
The formed nascent oxygen reacts with color substances and makes them colorless.
In case of Sulphur dioxide, it removes oxygen from the colored or dirty substances and makes them colorless.
But atmospheric oxygen slowly takes the place of the removed oxygen and because of which the material regains the color.

& S{{O}_{2}}+{{H}_{2}}O \rightleftharpoons {{H}_{2}}S{{O}_{3}} \rightleftharpoons 2{{H}^{+}}+SO_{3}^{-} \\\ & SO_{3}^{-}+[O]\to SO_{4}^{2-} \\\ & SO_{4}^{2-}+dye\to reduced\text{ }dye \\\ \end{aligned}$$ Sulphur dioxide acts as a temporary bleaching agent and removes oxygen by reduction as mentioned in the above reaction. But the large amount of oxygen present in the atmosphere slowly occupies the place of the removed oxygen then the material regains its color. Therefore Sulphur dioxide removes oxygen from the colored substances and makes them colorless through reduction process but it is a temporary action. **So, the correct option is B.** **Note:** Oxygen removes color from the clothes through the oxidation process and it is permanent. But sulphur dioxide removes color from the clothes through the reduction process and it is temporary. Therefore sulphur dioxide is a temporary bleaching agent.