Which of the following ligands will cause the smallest crystal field splitting?

In which of the following octahedral complex species the magnitude of $\Delta_0$ will be maximum?

Which one is correct for a high spin complex?

Match List-$I$ with List-$II$.
List-$I$ (Chromium $(III)$ Complexes) - List-$II$ ($\Delta_o$ $(cm^{-1})$)
$A$. $[Cr(CN)_6]^{3-}$ - $I$. $15,060$
$B$. $[CrF_6]^{3-}$ - $II$. $17,400$
$C$. $[Cr(H_2O)_6]^{3+}$ - $III$. $22,300$
$D$. $[Cr(en)_3]^{3+}$ - $IV$. $26,600$
Choose the correct answer from the options given below:

In potassium ferrocyanide,there are $..........$ pairs of electrons in the $t_{2g}$ set of orbitals.

Which of the following is the strongest field ligand?