Question

Which of the following is diamagnetic?

• A. Oxygen molecule
• B. Boron molecule
• C. ${N_2}^{+}$
• D. None of the above

Answer 1

Answer: (D)

In diamagnetic species all the electrons are paired when we write configuration according to molecular orbital theory. Whereas a paramagnetic species has at least one unpaired electron.
(i) $O_2=(8+8=16)$
$=\sigma 1s^2,{\sigma }^{\ast }1s^2,\sigma 2s^2,{\sigma }^{\ast }2s^2$, $\sigma 2p_z^2,\pi 2p_x^2,\pi 2p_y^2,{\pi }^{\ast }2p_x^1,{\pi }^{\ast }2p_y^1$
$\because$ It has two unpaired electrons.
$\therefore$ It is paramagnetic.
(ii) $B_2=(5+5=10)$
$=\sigma 1s^2,{\sigma }^{\ast }1s^2,\sigma 2s^2,{\sigma }^{\ast }2s^2$, $\pi 2p_x^1,\pi 2p_y^1$
$\because$ It has two unpaired electrons.
$\therefore$ It is paramagnetic.
(iii) $N_2^{+}=(7+7-1=13)=$
$\sigma 1s^2,{\sigma }^{\ast }1s^2,\sigma 2s^2,{\sigma }^{\ast }2s,\pi 2p_x^2,\pi p_y^2,\sigma p_z^1$
$\because$ It has one unpaired electron.
$\therefore$ It is paramagnetic.