Among [Ni(CO)4], [NiCl4]2–, [Co(NH3)4Cl2]Cl, Na3[CoF6], Na2O2 and CsO2, the total number of paramagnetic species is

To determine the number of paramagnetic species, we need to look at the electronic configuration of the central metal ion in each complex. Paramagnetic species have unpaired electrons, while diamagnetic species have all paired electrons.

1. [Ni(CO)4]: Ni in this complex is in 0 oxidation state. The electronic configuration of Ni is [Ar] 3d8 4s2. In [Ni(CO)4], Ni is in a low spin state due to the strong field ligand CO, and therefore, it is diamagnetic.

2. [NiCl4]2–: Ni in this complex is in +2 oxidation state. The electronic configuration of Ni2+ is [Ar] 3d8. Cl- is a weak field ligand and cannot cause pairing of electrons, so [NiCl4]2– is paramagnetic.

3. [Co(NH3)4Cl2]Cl: Co in this complex is in +3 oxidation state. The electronic configuration of Co3+ is [Ar] 3d6. NH3 is a strong field ligand and causes pairing of electrons, so [Co(NH3)4Cl2]Cl is diamagnetic.

4. Na3[CoF6]: Co in this complex is in +3 oxidation state. The electronic configuration of Co3+ is [Ar] 3d6. F- is a weak field ligand and cannot cause pairing of electrons, so Na3[CoF6] is paramagnetic.

5. Na2O2: This is a compound, not a complex. O2 in this compound has two unpaired electrons, so Na2O2 is paramagnetic.

6. CsO2: This is also a compound, not a complex. O2 in this compound has two unpaired electrons, so CsO2 is paramagnetic.

So, the total number of paramagnetic species among the given compounds and complexes is 4.