Total number of molecules/species from following which will be paramagnetic is __________.

$\mathrm{O}_2, \mathrm{O}_2^{+}, \mathrm{O}_2^{-}, \mathrm{NO}, \mathrm{NO}_2, \mathrm{CO}, \mathrm{K}_2\left[\mathrm{NiCl}_4\right],\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right] \mathrm{Cl}_3, \mathrm{~K}_2\left[\mathrm{Ni}(\mathrm{CN})_4\right]$

<p>To determine which molecules or species are paramagnetic, we need to identify those with unpaired electrons. Here's the analysis:</p> <p><p><strong>$\mathrm{O}_2$</strong>: This molecule has 2 unpaired electrons as predicted by the Molecular Orbital Theory (MOT), making it paramagnetic.</p></p> <p><p><strong>$\mathrm{O}_2^{+}$</strong>: This ion has 1 unpaired electron according to MOT, which also makes it paramagnetic.</p></p> <p><p><strong>$\mathrm{O}_2^{-}$</strong>: This ion contains 1 unpaired electron as determined by MOT, indicating it is paramagnetic.</p></p> <p><p><strong>$\mathrm{NO}$</strong>: As a species with an odd number of electrons, $\mathrm{NO}$ has unpaired electrons, making it paramagnetic.</p></p> <p><p><strong>$\mathrm{NO}_2$</strong>: This molecule is also an odd-electron species, which means it has unpaired electrons and is paramagnetic.</p></p> <p><p><strong>$\mathrm{K}_2\left[\mathrm{NiCl}_4\right]$</strong>: In this compound, $\mathrm{Ni}^{2+}$ (nickel with a +2 oxidation state) has an electron configuration of $3d^8$. Given the presence of weak field ligands and a coordination number of 4, this forms a tetrahedral complex. As a result, it is paramagnetic with 2 unpaired electrons.</p></p> <p>Thus, the paramagnetic species in the provided list are $\mathrm{O}_2$, $\mathrm{O}_2^{+}$, $\mathrm{O}_2^{-}$, $\mathrm{NO}$, $\mathrm{NO}_2$, and $\mathrm{K}_2\left[\mathrm{NiCl}_4\right]$.</p>