Chemical Bonding And Molecular Structure

Consider the following statements

I. In the conversion of $\mathrm{O}_2$ to $\mathrm{O}_2^{2+}$ bond order decreases.

II. In the conversion of $\mathrm{O}_2$ to $\mathrm{O}_2^{2+}$ magnetic property is not changed.

III. In the conversion of $\mathrm{O}_2$ to $\mathrm{O}_2^{2+}$ bond length decreases.

IV. $\mathrm{O}_2^{2-}$ and $\mathrm{B}_2$ have same bond order.

Identify the correct statements