Passivity of iron is due to the formation of

Identify the basic oxide from the following:

The number of ions from the following that have the ability to liberate hydrogen from a dilute acid is. . . . . . . .$Ti^{2+}, Cr^{2+}, V^{2+}$

Give examples and suggest reasons for the following features of the transition metal chemistry:
$(i)$ The lowest oxide of transition metal is basic,the highest is amphoteric/acidic.
$(ii)$ $A$ transition metal exhibits highest oxidation state in oxides and fluorides.
$(iii)$ The highest oxidation state is exhibited in oxoanions of a metal.

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

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