JEE MAIN - Chemistry (2025 - 28th January Evening Shift - No. 22)
Total number of molecules/species from following which will be paramagnetic is __________.
$\mathrm{O}_2, \mathrm{O}_2^{+}, \mathrm{O}_2^{-}, \mathrm{NO}, \mathrm{NO}_2, \mathrm{CO}, \mathrm{K}_2\left[\mathrm{NiCl}_4\right],\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right] \mathrm{Cl}_3, \mathrm{~K}_2\left[\mathrm{Ni}(\mathrm{CN})_4\right]$
$\mathrm{O}_2, \mathrm{O}_2^{+}, \mathrm{O}_2^{-}, \mathrm{NO}, \mathrm{NO}_2, \mathrm{CO}, \mathrm{K}_2\left[\mathrm{NiCl}_4\right],\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right] \mathrm{Cl}_3, \mathrm{~K}_2\left[\mathrm{Ni}(\mathrm{CN})_4\right]$
Answer
6
Explanation
$\mathrm{O}_2 \rightarrow 2$ unpaired electrons according to MOT
$\mathrm{O}_2{ }^{+} \rightarrow 1$ unpaired electrons according to MOT
$\mathrm{O}_2^{-} \rightarrow 1$ unpaired electrons according to MOT
$\mathrm{NO} \rightarrow$ odd electron species
$\mathrm{NO}_2 \rightarrow$ odd electron species
$\mathrm{K}_2\left[\mathrm{NiCl}_4\right] \rightarrow \mathrm{Ni}^{2+} \Rightarrow 3 \mathrm{~d}^8$ weak Ligand, C.N. $=4$
$\Rightarrow$ Tetrahedral, Paramagnetic with 2 unpaired electrons
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