The 'spin only' magnetic moment value of $\mathrm{MO}_4{ }^{2-}$ is ________ BM. (Where M is a metal having least metallic radii. among $\mathrm{Sc}, \mathrm{Ti}, \mathrm{V}, \mathrm{Cr}, \mathrm{Mn}$ and $\mathrm{Zn}$ ).

(Given atomic number: $\mathrm{Sc}=21, \mathrm{Ti}=22, \mathrm{~V}=23, \mathrm{Cr}=24, \mathrm{Mn}=25$ and $\mathrm{Zn}=30$)