Answer
Coordination number: $5$
Oxidation number: $+4$
Work Step by Step
The ligands ($O$ and $Cl_{4}$) that surround the central metal atom $Mo$ are 5. Thus, the coordination number is 5.
Let us suppose the oxidation number of $Mo$ is X. To find the oxidation number, we sum the known oxidation numbers and equal it to the charge on the complex.
$K_{2}$ = $ 2 \times (+1) $
$Cl_{4}$ = $ 4\times (-1) $
$O = -2 $
The overall charge is zero on the complex, thus:
$ 2 \times (+1) + X +( - 2)+ 4\times (-1) = 0 $
$+2 + X -2 - 4 =0 $
$ +2 +X -6 = 0$
$X= +6 -2$
$X= +4$
