Which of the following complex ions is diamagnetic in nature?

In which of the following orders are the given complex ions arranged correctly with respect to their decreasing spin-only magnetic moment?
$(i)$ $[FeF_{6}]^{3-}$
$(ii)$ $[Co(NH_{3})_{6}]^{3+}$
$(iii)$ $[NiCl_{4}]^{2-}$
$(iv)$ $[Cu(NH_{3})_{4}]^{2+}$

The correct match is:

Complexes	No. of unpaired electrons
$A. [CrF_6]^{4-}$	$P. 5$
$B. [MnF_6]^{4-}$	$Q. 2$
$C. [Cr(CN)_6]^{4-}$	$R. 1$
$D. [Mn(CN)_6]^{4-}$	$S. 4$

The metal ions that have the calculated spin-only magnetic moment value of $4.9 \ B.M.$ are:
$A. Cr^{2+}$ $B. Fe^{2+}$ $C. Fe^{3+}$ $D. Co^{2+}$ $E. Mn^{3+}$
Choose the correct answer from the options given below:

The total number of unpaired electrons present in the complex $K_3[Cr(C_2O_4)_3]$ is ..........

Which one has the highest paramagnetism?