Question

Which of the following statements is incorrect?

• A. The peroxide ion has a bond order of one
• B. The peroxide ion has a weaker bond than the oxygen molecule
• C. The peroxide ion as well as the dioxygen molecule are paramagnetic
• D. The bond length of peroxide ion is greater than that of the dioxygen molecule

Answer 1

The correct option is C The peroxide ion as well as the dioxygen molecule are paramagnetic

The electronic configuration $O_2$ molecule is:
$\left({\sigma }_{1s}{)}^2\right({\sigma }_{1s}^{\ast }{)}^2\left({\sigma }_{2s}{)}^2\right({\sigma }_{2s}^{\ast }{)}^2\left({\sigma }_{2pz}{)}^2\right({\pi }_{2px}{)}^2\left({\pi }_{2py}{)}^2\right({\pi }_{2px}^{\ast }{)}^1({\pi }_{2py}^{\ast }{)}^1$
The electronic configuration of peroxide $O_2^{2-}$ ion is:
$\left({\sigma }_{1s}{)}^2\right({\sigma }_{1s}^{\ast }{)}^2\left({\sigma }_{2s}{)}^2\right({\sigma }_{2s}^{\ast }{)}^2\left({\sigma }_{2pz}{)}^2\right({\pi }_{2px}{)}^2\left({\pi }_{2py}{)}^2\right({\pi }_{2px}^{\ast }{)}^2({\pi }_{2py}^{\ast }{)}^2$

We know,
Bond order of $O_2^{2-}=\frac{1}{2}(10-8)=1$
Bond order of $O_2=\frac{1}{2}(10-6)=2$
Since the bond order of $O_2$ is more compared to that of $O_2^{2-}$, the peroxide ion has a weaker bond than the dioxygen molecule.

Species having unpaired electrons generally show paramagnetism. Since, $O_2^{2-}$ does not possesses any unpaired electrons, it is not paramagnetic in nature.

Higher the bond order, shorter is the bond length. Since, the bond order of peroxide ion is less, the bond length of the peroxide ion is greater than that of the dioxygen molecule.