The metal present in the ions,$Cr{O}_4^{2-},Mn{O}_4^{-}andV{O}_4^{3-}$ , when arranged in the decreasing order of their oxidation states follows the order

$x\to x=+7$

$Cr{O}_4^{2-}\Rightarrow 1\times x+4\times \left(-2\right)=-2$

$x\Rightarrow x=+6$

$V{O}_4^{3-}\Rightarrow x\times 1+4\times \left(-2\right)=-3$

$x\Rightarrow x=+5$

So, decreasing order of oxidation – State is follow as $Mn>Cr>V$ .