Identify species having metal atom in $+6$ oxidation state from following

Let $x$ be the oxidation state of the metal atom in each species.

For $\text{MnO}_4^-$, the oxidation state of Mn is calculated as:
$x + 4(-2) = -1 \Rightarrow x = +7$

For $[\text{Cr}(\text{CN})_6]^{3-}$, the oxidation state of Cr is calculated as:
$x + 6(-1) = -3 \Rightarrow x = +3$

For $\text{Cr}_2\text{O}_3$, the oxidation state of Cr is calculated as:
$2x + 3(-2) = 0 \Rightarrow x = +3$

For $\text{CrO}_2\text{Cl}_2$, the oxidation state of Cr is calculated as:
$x + 2(-2) + 2(-1) = 0 \Rightarrow x - 6 = 0 \Rightarrow x = +6$

Thus, $\text{CrO}_2\text{Cl}_2$ has the metal atom in the $+6$ oxidation state.

Answer: $\text{CrO}_2\text{Cl}_2$