The crystal field-splitting for ${\mathrm{Cr}}^{3+}$ ion in octahedral field changes for ligands ${\mathrm{I}}^{-},{\mathrm{H}}_2\mathrm{O},{\mathrm{NH}}_3,{\mathrm{CN}}^{-}$ in increasing order is :

According to the spectrochemical series, the order of the ligands that cause an increase in the crystal field-splitting for the Cr³⁺ ion in an octahedral field is,

$\begin{array}{r}{\mathrm{I}}^{-}<{\mathrm{H}}_2\mathrm{O}<{\mathrm{NH}}_3<{\mathrm{CN}}^{-}\end{array}$

So, the correct option is A.