The formation of the oxide ion O^2-(g) requires first an exothermic and then an endothermic step as shown below

O_(g) + e^- = $$O_{(g)}^{-}$$ $$\Delta $$H^o = -142 kJmol^-1

$$O_{(g)}^{-}$$ + e^- = $$O_{(g)}^{2-}$$ $$\Delta $$H^o = 844 kJmol^-1

This because

Which one of the following is an amphoteric oxide?

According to the Periodic Law of elements, the variation in properties of elements is related to their

The atomic numbers of Vanadium (V), Chromium (cr), Manganese (Mn) and Iron (Fe), respectively, $$23,24,25$$ and $$26$$. Which one of these may be expected to have the higher second ionization enthalpy?