Specify the oxidation numbers of the metals in the following coordination entities:
$(i) [Co(H_{2}O)(CN)(en)_{2}]^{2+}$
$(ii) [CoBr_{2}(en)_{2}]^{+}$
$(iii) [PtCl_{4}]^{2-}$
$(iv) K_{3}[Fe(CN)_{6}]$
$(v) [Cr(NH_{3})_{3}Cl_{3}]$

(N/A) $(i) [Co(H_{2}O)(CN)(en)_{2}]^{2+}$
Let the oxidation number of $Co$ be $x$.
The charge on the complex is $+2$.
$x + 0 + (-1) + 2(0) = +2$
$x - 1 = +2$
$x = +3$
$(ii) [CoBr_{2}(en)_{2}]^{+}$
Let the oxidation number of $Co$ be $x$.
The charge on the complex is $+1$.
$x + 2(-1) + 2(0) = +1$
$x - 2 = +1$
$x = +3$
$(iii) [PtCl_{4}]^{2-}$
Let the oxidation number of $Pt$ be $x$.
The charge on the complex is $-2$.
$x + 4(-1) = -2$
$x - 4 = -2$
$x = +2$
$(iv) K_{3}[Fe(CN)_{6}]$
Let the oxidation number of $Fe$ be $x$.
The charge on the complex $[Fe(CN)_{6}]$ is $-3$.
$x + 6(-1) = -3$
$x - 6 = -3$
$x = +3$
$(v) [Cr(NH_{3})_{3}Cl_{3}]$
Let the oxidation number of $Cr$ be $x$.
The complex is neutral,so its total charge is $0$.
$x + 3(0) + 3(-1) = 0$
$x - 3 = 0$
$x = +3$