Question

Which of the following molecules/species have identical bond order and magnetic properties?
(I) $O_2^{+}$
(II) $NO$
(III) $N_2^{+}$

• A. (II) and (III) only
• B. (I), (II) and (III)
• C. (I), (II) only
• D. (I), (III) only

Answer 1

The correct option is B (I), (II) and (III)

(I) $O_2^{+}:\left(\sigma 1s{)}^2\right({\sigma }^{\ast }1s{)}^2\left(\sigma 2s{)}^2\right({\sigma }^{\ast }2s{)}^2\left(\sigma 2p_z{)}^2\right(\pi 2p_x^2=\pi 2p_y^2\left)\right({\pi }^{\ast }2p_x^1={\pi }^{\ast }2p_y^0)$
Bond order = $\frac{1}{2}(10-5)=2.5$

(II) $NO$ is isoelectronic with $O_2^{+}$ :
$\left(\sigma 1s{)}^2\right({\sigma }^{\ast }1s{)}^2\left(\sigma 2s{)}^2\right({\sigma }^{\ast }2s{)}^2(\pi 2p_x^2=\pi 2p_y^2)\left(\sigma 2p_z{)}^2\right({\pi }^{\ast }2p_x^1={\pi }^{\ast }2p_y^0)$
Bond order = $\frac{1}{2}(10-5)=2.5$

(III) $N_2^{+}:\left(\sigma 1s{)}^2\right({\sigma }^{\ast }1s{)}^2\left(\sigma 2s{)}^2\right({\sigma }^{\ast }2s{)}^2(\pi 2p_x^2=\pi 2p_y^2)(\sigma 2p_z{)}^1$
Bond order = $\frac{1}{2}(9-4)=2.5$

$O_2^{+},NO$ and $N_2^{+}$ have the same bond order i.e, 2.5 and have the same magnetic property having one unpaired electron.