Answer
Coordination number: 6
Oxidation number: +4
Work Step by Step
The ligand $(en)_{3}$ that surround the central metal atom $Pt$ are 3, but since $en$ is a bidentate ligand, the coordination number is 6. ($3×2=6$)
Let us suppose the oxidation number of $Pt$ is X. To find the oxidation number, we sum the known oxidation numbers and equal it to the charge on the complex.
Also,
$(en)_{3} = 3 \times (0)$
$(ClO_{4})_{4} = 4 \times (-1)$
The overall charge is zero on the complex, thus:
$X+ 3 \times (0) + 4 \times (-1)= 0$
$X +0 -4 = 0$
$X-4=0$
$X=+4$
The oxidation number of $Pt$ is +4
