Among ${\mathrm{Co}}^{3+},{\mathrm{Ti}}^{2+},{\mathrm{V}}^{2+}$ and ${\mathrm{Cr}}^{2+}$ ions, one if used as a reagent cannot liberate ${\mathrm{H}}_2$ from dilute mineral acid solution, its spin-only magnetic moment in gaseous state is _____  B.M. (Nearest integer)