AIPMT 2010 Physics and Chemistry Paper

In case of high spin complex, ∆0 is small. Thus, the energy required to pair up the fourth electron with the electrons of lower energy d-orbitals would be higher than that required to place the electrons in the higher d4 orbital. Thus, pairing does not occur.
For high spin d4 octahedral complex,∴ Crystal field stabilisation energy
=(−3×0.4+1×0.6)∆0
=(−1.2+0.6)∆0
=−0.6∆0