Among the following species,the one which causes the highest $CFSE, \Delta _0$ as a ligand is

$CuSO_4 \cdot 5 H_2O$ is blue in colour while $CuSO_4$ is colourless. Why?

Which sets of the $d$-orbitals are directly oriented towards the ligands in octahedral coordination compounds?

Which of the following ion configurations has zero $CFSE$ in both strong and weak field ligands in an octahedral complex?

How many of the following ligands are stronger than $H_2O$? $S^{2-}$,$Br^{-}$,$C_2O_4^{2-}$,$CN^{-}$,$en$,$NH_3$,$CO$,$OH^{-}$

For an octahedral complex,which of the following $d-$electronic configuration will give the maximum magnitude of crystal field stabilization energy,in terms of $\Delta_{o}$?