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

\(CrO_2Cl_2\)

The correct answer is option 4. \(CrO_2Cl_2\).

To identify the species with an atom in the +6 oxidation state, we need to determine the oxidation state of the central atom in each species. Here’s a step-by-step breakdown for each compound:

\(MnO_4^-\) (Permanganate ion):

Oxygen \((O)\) typically has an oxidation state of \(-2\).

Let \( x \) be the oxidation state of manganese \((Mn)\).

The total charge of the ion is \(-1\).

The equation for the oxidation states is:

\( x + 4(-2) = -1 \)

\(⇒ x - 8 = -1 \)

\(⇒ x = +7 \)

Manganese in \(MnO_4^-\) is in the \(+7\) oxidation state.

2. \([Cr(CN)_6]^{3-}\) (Hexacyanochromate(III) ion):

Cyanide \((CN)\) has an oxidation state of \(-1\).

Let \( x \) be the oxidation state of chromium (Cr).

The total charge of the ion is \(-3\).

The equation for the oxidation states is:

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

\(⇒ x - 6 = -3 \)

\(⇒ x = +3 \)

Chromium in \([Cr(CN)_6]^{3-}\) is in the \(+3\) oxidation state.

3. \([NiF_6]^{2+}\) (Hexafluoronickelate(IV) ion):

Fluorine \((F)\) typically has an oxidation state of \(-1\).

Let \( x \) be the oxidation state of nickel (Ni).

The total charge of the ion is \(-2\).

The equation for the oxidation states is:

\( x + 6(-1) = -2 \)

\(⇒ x - 6 = -2 \)

\(⇒ x = +4 \)

Nickel in \([NiF_6]^{2+}\) is in the \(+4\) oxidation state.

4. \(CrO_2Cl_2\) (Chromyl chloride):

Oxygen \((O)\) typically has an oxidation state of \(-2\).

Chlorine \((Cl)\) typically has an oxidation state of \(-1\).

Let \( x \) be the oxidation state of chromium \((Cr)\).

The compound is neutral, so the sum of the oxidation states must be \(0\).

The equation for the oxidation states is:

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

\(⇒ x - 4 - 2 = 0 \)

\(⇒ x = +6 \)

Chromium in \(CrO_2Cl_2\) is in the \(+6\) oxidation state.

From this analysis, the species with an atom in the +6 oxidation state is \(CrO_2Cl_2\).