Question

leaching of gold or silver involves a disproportionation reaction justify

I have exam today. Please explain.....

Answer 1

Actually disproportionate reaction means reaction in which a compound goes in oxidation and reduction both.
In leaching process of gold, reaction is
the monovalent tends to disproportionate according to the following reaction:

Here we can see that initially Au was in +1 oxidation state which changes into +3 and 0,
from this we can say that leaching is a disproportionate reaction.
Similar process is carried out in silver.