Explanation:

Paramagnetic behavior is the tendency of a molecule to be attracted by an external magnetic field. When an external magnetic field is applied, the electrons in the molecule align themselves in the direction of the magnetic field, resulting in a net magnetic moment. The magnitude of this magnetic moment is directly related to the number of unpaired electrons in the molecule. The greater the number of unpaired electrons, the higher the magnetic moment, and the more paramagnetic the molecule.

The given complexes are all cyano complexes with a formula of MX6, where M is a metal ion and X is a cyano ligand (-CN). The metal ions in these complexes are transition metals, which have partially filled d-orbitals that can accommodate unpaired electrons.

To determine the complex with the lowest paramagnetic behavior, we need to find the complex with the least number of unpaired electrons, i.e., the complex with the lowest number of electrons occupying the d-orbitals. This is because the cyano ligand is a strong field ligand, which causes the d-orbitals to split into higher energy (e.g., dx2-y2 and dz2) and lower energy (e.g., dxy, dyz, and dxz) orbitals. The electrons occupy the lower energy orbitals first before filling the higher energy orbitals. Therefore, the complex with the lowest number of electrons occupying the d-orbitals will have the least number of electrons occupying the higher energy orbitals, resulting in the lowest paramagnetic behavior.

Answer:

The complex with the lowest value of paramagnetic behavior is [Co(CN)6]3-. This is because cobalt (Co) has the lowest number of d-electrons (27) among the given metal ions, and the cyano ligand is a strong field ligand that causes a large splitting of the d-orbitals. As a result, the electrons occupy the lower energy orbitals first, and only two electrons occupy the higher energy orbitals, resulting in the lowest value of paramagnetic behavior.