$Cr ^{3+}=62\,pm$ radius
$Mn ^{+3}=65\, pm$ radius
$Fe ^{+3}=65\, pm$ radius
So, $Cr ^{3+}$ has highest tendency to attract ligand.
(પરમાણુ ક્રમાંક $Cr = 24, Mn = 25, $$Fe = 26, Ni = 28$)
$(i)$ $\left[ M ( NCS )_{6}\right]^{(-6+ n )}$
$(ii)$ $\left[ MF _{6}\right]^{(-6+ n )}$
$(iii)$ $\left[ M \left( NH _{3}\right)_{6}\right]^{ n ^{+}}$