The oxidation number of the underlined atom in the following species. Identify the incorrect option.

Options

A. `Cu_2underlineO` is -1
B. `underlineClO_3^-` is +5
C. K_2underline(Cr)_2O_7` is +6
D. `Hunderline(Au)Cl_4` is +3

Answer

To determine the incorrect option regarding the oxidation number of the underlined atom in the given species, we will analyze each option step by step.

### Step 1: Analyze Cu2O
- **Identify the species**: Cu2O
- **Identify the underlined atom**: Oxygen (O)
- **Assign oxidation states**: Oxygen typically has an oxidation state of -2.
- **Set up the equation**: Let the oxidation state of copper (Cu) be \( x \).

The equation based on the compound's neutrality:
\[ 2x + (-2) = 0 \]
Solving for \( x \):
\[ 2x - 2 = 0 \implies 2x = 2 \implies x = +1 \]

- **Conclusion**: The oxidation state of Cu is +1 and for O is -2. However, if the question states the oxidation state of oxygen as -1, this is incorrect.

### Step 2: Analyze ClO3^-
- **Identify the species**: ClO3^-
- **Identify the underlined atom**: Chlorine (Cl)
- **Assign oxidation states**: Oxygen has an oxidation state of -2.
- **Set up the equation**: Let the oxidation state of chlorine be \( x \).

The equation based on the charge of the ion:
\[ x + 3(-2) = -1 \]
Solving for \( x \):
\[ x - 6 = -1 \implies x = +5 \]

- **Conclusion**: The oxidation state of Cl is +5, which is correct as per the given option.

### Step 3: Analyze K2Cr2O7
- **Identify the species**: K2Cr2O7
- **Identify the underlined atom**: Chromium (Cr)
- **Assign oxidation states**: Oxygen has an oxidation state of -2.
- **Set up the equation**: Let the oxidation state of chromium be \( x \).

The equation based on the charge of the compound:
\[ 2(+1) + 2x + 7(-2) = 0 \]
Solving for \( x \):
\[ 2 + 2x - 14 = 0 \implies 2x - 12 = 0 \implies 2x = 12 \implies x = +6 \]

- **Conclusion**: The oxidation state of Cr is +6, which is correct as per the given option.

### Step 4: Analyze AuCl4^-
- **Identify the species**: AuCl4^-
- **Identify the underlined atom**: Gold (Au)
- **Assign oxidation states**: Chlorine has an oxidation state of -1.
- **Set up the equation**: Let the oxidation state of gold be \( x \).

The equation based on the charge of the ion:
\[ x + 4(-1) = -1 \]
Solving for \( x \):
\[ x - 4 = -1 \implies x = +3 \]

- **Conclusion**: The oxidation state of Au is +3, which is correct as per the given option.

### Final Conclusion
The incorrect option is **option A** (Cu2O), where the oxidation state of oxygen was incorrectly stated as -1 instead of -2.