Total number of molecules/species from the following which will be paramagnetic is ________________________.
\[
O_2, O_2^+, O_2^-, NO, NO_2, CO, K_2[NiCl_4], [Co(NH_3)_6]Cl_3, K_2[Ni(CN)_4]
\]
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Molecular orbital theory helps determine paramagnetic behavior based on unpaired electrons.