Question

------ turns acidified potassium permanganate from purple to colourless.
A. ${\text{C}}{{\text{O}}_{\text{2}}}$
B. ${{\text{H}}_{\text{2}}}{\text{O}}$
C. ${\text{C}}{{\text{l}}_{\text{2}}}$
D. ${\text{S}}{{\text{O}}_{\text{2}}}$

Answer 1

Hint: The reactions in which the colour change of compound occurs are mostly redox reactions. In these reactions the oxidation number of metal ions is changed which changes its colour absorbing power and hence the solution becomes colourless.

Complete step by step answer:
The removal of electrons, or addition of oxygen atom or removal of hydrogen atom is known as oxidation. And the opposite of this, removal of oxygen atom or addition of hydrogen atom or addition of electron is reduction. And when both the processes oxidation and reduction occur in one reaction then the overall reaction is known as redox reaction. In some cases the colour change is the result of redox reactions.
The colour change occurs because as the oxidation state of metal increases the splitting of d orbitals increases which changes the tendency of compound to absorb colours and the colour it absorbs we see, in this way oxidation and reduction affects the colour of complex.
As we all know that acidified potassium permanganate is a strong oxidizing agent, so the only function of this in reactions is to oxidize the other compounds and reduce itself. The potassium permanganate is purple in colour but after the reaction it becomes colourless, this happens because as the sulphur dioxide gas (${\text{S}}{{\text{O}}_{\text{2}}}$) passes through the solution in the form of bubbles and the whole solution becomes colourless, the manganate ($VII$) is reduced to manganate ($II$) ions which is the cause of colour change of the solution.
Hence we can conclude that sulphur dioxide (${\text{S}}{{\text{O}}_{\text{2}}}$) turns acidified potassium permanganate from purple to colourless.

So, the correct answer is Option D .

Note:
As we all know that during compound formations various changes are seen in the orbitals, electrons change their positions, replace each other and many more things. But the colour of compound occurs due to splitting of d orbitals, they absorb visible wavelengths and hence we are able to see them.