The 'spin only' magnetic moment value of \( \mathrm{MO_4^{2-}} \) is ______ \( \mathrm{BM} \).
(Where \( \mathrm{M} \) is a metal having least metallic radii among Sc, Ti, V. Cr. Mn and Zn)
[Given atomic number : Sc \( = 21 \), Ti \( = 22 \), V \( = 23 \), Cr \( = 24 \), Mn \( = 25 \) and Zn \( = 30 \)]