Q. What is Pairing energy explain?

Pairing energy, P, depends mainly on the electronic distribution of the central metal ion and its value can be obtained from the atomic spectra of the element. The D₀ obtained from the molecular spectra of the complex. It depends on the metal ion, ligand and the geometry of the complex. Once these two values are known for any complex, you will know whether it will be high spin or low spin and you will also be able to calculate the CFSE. Table 14.6 gives the pairing energy values ford to d7 ions of first row transition elements as well as values for a few complexes. In d^l,d ², d³, d⁸. d⁹ and d^l0 systems only one configuration each  is possible.