Which of the following does not give oxygen on heating?

$A$ purple colored compound of Manganese $(X)$ decomposes on heating to liberate oxygen and forms compounds of Manganese $(Y)$ and $(Z)$. Compound $(Z)$ reacts with $KOH$ in the presence of potassium nitrate to give compound $(Y)$. Compounds $(X)$,$(Y)$,and $(Z)$ respectively are:

What are the oxidation states of iron in the minerals hematite and magnetite?

Pick out the incorrect statement:

The transition metal which forms a green compound in $+3$ oxidation state and a yellow-orange compound in $+6$ oxidation state is

The yellow colour of chromates changes to orange on acidification due to the formation of: