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