When $CuSO_4$ reacts with $KI$,the oxidation number of $Cu$ changes by

$Zn_{(s)} + CuSO_{4(aq)} \rightarrow ZnSO_{4(aq)} + Cu_{(s)}$ is an example of which type of process?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$BaSO_3(s) + H_2SO_4(aq) \longrightarrow BaSO_4(s) + SO_2(g) + H_2O(l)$

To an acidified dichromate solution,a pinch of $Na_2O_2$ is added and shaken. What is observed?

When silver nitrate is heated to red hot,what is formed?

How do you account for the following observations?
$(a)$ Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants,yet in the manufacture of benzoic acid from toluene,we use alcoholic potassium permanganate as an oxidant. Why? Write a balanced redox equation for the reaction.
$(b)$ When concentrated sulphuric acid is added to an inorganic mixture containing chloride,we get a colourless pungent-smelling gas $HCl$,but if the mixture contains bromide,then we get red vapour of bromine. Why?