In \(\left[ MnCl _4\right]^2: d^5\) configuration and \(5\) unpaired electrons
In \(\left[ CoCl _4\right]^2: d^7\) configuration and \(3\) unpaired electrons
In \(\left[ Fe ( CN )_6\right]^4: d ^6\) configuration, low spin complex and o unpaired electrons
More the number of unpaired electrons, more the value of magnetic moment.
Hence, the order is \(\left[ MnCl _4\right]^{2-} > \left[ CoCl _4\right]^{2-} > \left[ Fe ( CN )_6\right]^{4-}\)
$(i)\, [CoCl_3 (NH_3)_3]$ $(ii)\, [Co(en)_3]Cl_3$
$(iii)\, [Co(C_2O_4)_2(NH_3)_2]^-$ $(iv)\, [CrCl_2(NH_3)_2(en)]^+$