Which of the following statements is not correct?

oxidation state of \(O\) in \(OH^-\) is \(+1\)

The correct answer is option 1. oxidation state of \(O\) in \(OH^-\) is \(+1\).

Let us examine each statement in detail and explain the reasoning behind the oxidation states of oxygen in different compounds and ions.

1. Oxidation state of \(O\) in \(OH^-\) is \(+1\)

Compound: \(OH^-\) (hydroxide ion)

Analysis:

The overall charge of the hydroxide ion is -1.

The oxidation state of hydrogen \((H)\) in most compounds, including \(OH^-\), is +1.

To determine the oxidation state of oxygen \((O)\), we use the fact that the sum of the oxidation states in the ion must equal the overall charge of the ion.

Let \(x\) be the oxidation state of oxygen:

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

Solving for \(x\):

\(x = -1 - 1\)

\(x = -2\)

Therefore, the oxidation state of oxygen in \(OH^-\) is -2, not +1. This statement is incorrect.

2. Oxidation state of \(O\) in \(OF_2\) is \(+2\)

Compound: \(OF_2\) (oxygen difluoride)

Analysis:

Fluorine (F) is the most electronegative element and always has an oxidation state of -1 in compounds.

There are two fluorine atoms, so the total contribution to the oxidation state by fluorine is:

\(2 \times (-1) = -2\)

Let \(x\) be the oxidation state of oxygen:

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

Solving for \(x\):

\(x - 2 = 0\)

\(x = 2\)

Therefore, the oxidation state of oxygen in \(OF_2\) is +2. This statement is correct.

3. Oxidation state of \(O\) in superoxide is \(-1/2\)

Compound: \(O_2^-\) (superoxide ion)

Analysis:

The superoxide ion has an overall charge of -1.

There are two oxygen atoms in the superoxide ion.

Let \(x\) be the oxidation state of each oxygen atom:

\(2(x) = -1\)

Solving for \(x\):

\(x = -\frac{1}{2}\)

Therefore, the oxidation state of each oxygen atom in superoxide is -1/2. This statement is correct.

4. Oxidation state of \(O\) in \(O^{2-}\) is \(-2\)

Compound: \(O^{2-}\) (oxide ion)

Analysis:

The oxide ion has an overall charge of -2.

In the oxide ion, there is only one oxygen atom.

The oxidation state of oxygen is the same as the charge of the ion:

\(\text{Oxidation state of } O = -2\)

Therefore, the oxidation state of oxygen in \(O^{2-}\) is -2. This statement is correct.

The incorrect statement is: (1) Oxidation state of \(O\) in \(OH^-\) is \(+1\).

The correct oxidation state of oxygen in \(OH^-\) is -2.