How are transition metals and their oxides used in industrial processes?

The ${E^0}_{M^{3+}/M^{2+}}$ values for $Cr, Mn, Fe$ and $Co$ are $-0.41, +1.57, +0.77$ and $+1.97 \ V$ respectively. For which one of these metals is the change in oxidation state from $+2$ to $+3$ the easiest?

Which of the following pairs of oxides is amphoteric in nature?

Iron is rendered passive by the action of

What is the correct order of basic character for the following transition metal monoxides?

Identify the correct statement about properties of interstitial compounds.