Question

Which of the following species the longest $O-O$ bond length ?

• A. $O_2$
• B. $O_2^{+}$
• C. $O_2^{-}$
• D. $O_2^{2-}$

Answer 1

The correct option is D $O_2^{2-}$

	$O_2$	$O_2^{+}$	$O_2^{-}$	$O_2^{2-}$
Bond order	$=\frac{8-4}{2}$ $=2$	$=\frac{8-3}{2}$ $=2.5$	$=\frac{8-5}{2}$ $=1.5$	$=\frac{8-6}{2}$ $=1$

Since $O_2^{2-}$ has the lowest Bond order the $O-O$ bond is the longest in case of $O_2^{2-}$, due to the fact that Bond order $\propto \frac{1}{Bondlength}$