Question

One gas bleaches the colored matter by reduction temporary while the other one by oxidation permanently. The gases are respectively:
A.$S{O_2}$ and $C{l_2}$
B.${O_3}$ and $C{l_2}$
C.${H_2}$ and $C{O_2}$
D.$C{l_2}$ and $C{O_2}$

Answer 1

Hint:
Oxidation is the process in which there is a removal of an electron and whereas in reduction there is an addition of an electron. In oxidation energy is released whereas in case of reduction energy is stored.

Complete answer:
A)
The only gas that bleaches coloring matter by reduction is sulphur dioxide gas.
It shows its bleaching properties in the presence of moisture.
The reaction of sulphur dioxide is as follows:
$S{O_2} + 2{H_2}O \to {H_2}S{O_4} + 2\left[ H \right]$
When colored matter reacts with nascent hydrogen the reaction is as follows:
Colored matter $ + 2\left[ H \right] \to $ colorless color(in the presence of air)
When sulphur dioxide reacts with water it forms sulphuric acid and nascent hydrogen and also releases oxygen.
When these nascent hydrogen comes in contact with colored matter in the presence of air, it loses its color.
It regains its color once the atmospheric oxygen takes the place of the released oxygen.
Thus sulphur dioxide gas bleaches the colored matter temporarily.
B)
The only gas that bleaches coloring matter by oxidation permanently is chlorine gas.
The reaction of chlorine gas is as follows:
$C{l_2} + {H_2}O \to HCl + HClO$
When chlorine gas reacts with water it gives hydrochloric acid and hypochlorous acid.
$HClO \to HCl + \left[ O \right]$
Hypochlorous acid is highly unstable, thus it dissociates and gives nascent oxygen.
When nascent oxygen reacts with colored matter , the reaction is as follows:
$\left[ O \right] + $colored matter$ \to $ colorless
This nascent oxygen when reacted with colored matter, it turns the matter colorless permanently.
It is a permanent process because chlorine gas is a powerful oxidizing agent.

Therefore, the correct answer is option A i.e $S{O_2}$and $C{l_2}$ .

Note:Nascent hydrogen is less reactive compared to nascent oxygen. Nascent hydrogen is stable at room temperatures whereas nascent oxygen is highly unstable at room temperatures. Nascent hydrogen when reacts with coloring matter it turns matter colorless for a short period of time whereas nascent oxygen when comes in contact with coloring matter it turns the matter colorless permanently.