Ferrous sulphate on heating gives

Which of the following characteristics of the transition metals is associated with their catalytic activity?

Oxygen is absorbed by molten $Ag$,which is evolved on cooling and the silver particles are scattered,this phenomenon is known as

On adding $KI$ to a solution of copper sulphate,what happens?

Which element can have oxidation state from $4$ to $6$?

The incorrect statement$(s)$ among $(a)-(c)$ is (are) :-
$(a)$ $W(VI)$ is more stable than $Cr(VI)$
$(b)$ In the presence of $HCl$,permanganate titrations provide satisfactory results.
$(c)$ Some lanthanoid oxides can be used as phosphors.