The species with spin only magnetic moment of $\sqrt{24}$ BM is :

$\begin{array}{l}\left[{\mathrm{CoF}}_3{\left({\mathrm{H}}_2\mathrm{O}\right)}_3\right]\text{ has }4\text{ unpaired electrons. So, }\mathrm{MM}\to \sqrt{24}\mathrm{BM}\\ {\left[{\mathrm{CoCl}}_4\right]}^{2-}\text{ has }3\text{ unpaired electrons. }\\ {\left[{\mathrm{NiCl}}_4\right]}^{2-}\text{. has }2\text{ unpaired electrons. }\\ {\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{2+}\text{ has }2\text{ unpaired electrons. }\end{array}$