CFSE Questions

The $d$ -electron configurations of ${\text{Cr}}^{2+}$, ${\text{Mn}}^{2+}$, ${\text{Fe}}^{2+}$ and ${\text{Ni}}^{2+}$ are $3d^4$, $3d^5$, $3d^6$ and $3d^8$ respectively. Which one of the following aqua complexes will exhibit the minimum paramagnetic behaviour?

In which of the following coordination entities the magnitude of ${\Delta }_O$ (CFSE in octahedral field) will be maximum?

Crystal field stabilization energy for high spin $d^4$ octahedral complex is:

Among the following complexes, the one which shows Zero crystal field stabilisation energy (CFSE) is: