Ferrous and ferric ions in solution may be distinguished by using

In the reaction between moist $SO_2$ and acidified permanganate solution:

On treating $SO_2$ with an aqueous solution of $KMnO_4$,the manganese ion reduces to

$KI$ is oxidised into $I_2$ by using the reagent

If salt $Q$ undergoes a redox reaction with $H_2S$ in an acidic medium,then which of the following species cannot be a possible product?

Whenever a reaction between an oxidising agent and a reducing agent is carried out,a compound of lower oxidation state is formed if the reducing agent is in excess and a compound of higher oxidation state is formed if the oxidising agent is in excess. Justify this statement giving three illustrations.