Which one of the following will show paramagnetism corresponding to 2 unpaired electrons?(Atomic numbers: Ni=28,Fe=26)[FeF6]3−[NiCl4]2−[Fe(CN)6]3−[Ni(CN)4]2−

To answer this question, we need to understand the concept of paramagnetism and the electronic configuration of the given compounds.

Paramagnetism is a form of magnetism whereby some materials are attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. This is due to the presence of unpaired electrons in the atomic or molecular electron cloud.

1. [FeF6]3−: The oxidation state of Fe in this compound is +3. The atomic number of Fe is 26, so its electronic configuration is [Ar] 3d6 4s2. In the +3 oxidation state, it loses 3 electrons, 2 from the 4s and 1 from the 3d, leaving it with 5 electrons in the 3d orbital. Therefore, it has 5 unpaired electrons.

2. [NiCl4]2−: The oxidation state of Ni in this compound is +2. The atomic number of Ni is 28, so its electronic configuration is [Ar] 3d8 4s2. In the +2 oxidation state, it loses 2 electrons from the 4s orbital, leaving it with 8 electrons in the 3d orbital. Therefore, it has 2 unpaired electrons.

3. [Fe(CN)6]3−: The oxidation state of Fe in this compound is +3. As explained above, it has 5 unpaired electrons.

4. [Ni(CN)4]2−: The oxidation state of Ni in this compound is +2. As explained above, it has 2 unpaired electrons.

Therefore, the compounds [NiCl4]2− and [Ni(CN)4]2− will show paramagnetism corresponding to 2 unpaired electrons.