Q25 / 180 · COMEDK 2018 · Chemistry

Which of the following is diamagnetic?

  • A
    $\mathrm{H}_{2}^{+} \quad$
  • B
    $\mathrm{O}_{2} \quad$
  • Correct answer
    C
    $\mathrm{Li}_{2} \quad$
  • D
    $\mathrm{He}_{2}^{+}$

Solution

$\mathrm{H}_{2}^{+}$and $\mathrm{He}_{2}^{+}$contains odd number of electrons $\therefore$ They are paramagnetic. Among $\mathrm{Li}_{2}$ and $\mathrm{O}_{2}$ $\operatorname{Li}_{2}(6)=\sigma 1 s^{2}, \sigma 1 s^{2}, \sigma 2 s^{2}$ Li have no unpaired electron. $\therefore$ It is diamagnetic $\mathrm{O}_{2}(18)=\sigma 1 s^{2}, \sigma 1 s^{2}, \sigma 2 s^{2}, \sigma 2 s^{2} \pi 2 p_{x}^{2}=\pi 2 p_{y}^{2}$ $$ \sigma 2 p_{z}^{2}, \pi^{*} 2 p_{x}^{1}=\pi^{3} 2 p_{z}^{1} $$ It has two unpaired electrons. So, it is paramagnetic.

Hence, the correct answer is option: 'C'.

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