$N{a_3}[Fe{F_6}]$    $\to $   $s{p^3}{d^2}$   hybridisation $\to $  $3$ unpaired electrons

$[Cr{({H_2}O)_6}]S{O_4}$    $\to $  ${d^2}s{p^3}$   hybridisation $\to $  $3$ unpaired electrons

${K_4}[Fe{(CN)_6}]$ $\to $      ${d^2}s{p^3}$   hybridisation  $\to $ No unpaired electrons

Zero magnetic moment means all the electrons paired.