Amongst the following, identify the species with an atom in +6 oxidation state.

For $$CrO_2Cl_2$$ (Chromyl chloride):

Let the oxidation state of $$Cr$$ be $$x$$. 

$$x + 2(\text{O.S. of } O) + 2(\text{O.S. of } Cl) = 0$$

$$x + 2(-2) + 2(-1) = 0$$

$$x - 4 - 2 = 0 \implies x = +6$$

For $$[Cr(CN)_6]^{3-}$$: 

Let the oxidation state of $$Cr$$ be $$x$$. 

$$x + 6(\text{O.S. of } CN) = -3$$

$$x + 6(-1) = -3$$

$$x - 6 = -3 \implies x = +3$$

For $$Cr_2O_3$$:

Let the oxidation state of $$Cr$$ be $$x$$. 

$$2x + 3(\text{O.S. of } O) = 0$$

$$2x + 3(-2) = 0$$

$$2x = 6 \implies x = +3$$

For $$[MnO_4]^-$$ (Permanganate ion):

Let the oxidation state of $$Mn$$ be $$y$$. 

$$y + 4(\text{O.S. of } O) = -1$$

$$y + 4(-2) = -1$$

$$y - 8 = -1 \implies y = +7$$