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 oxidation number from the given species, we need to analyze each option step by step. Let's go through each species and calculate the oxidation numbers.

### Step 1: Analyze Cu2O
- **Compound**: Cu2O
- **Element underlined**: O (Oxygen)
- **Oxidation state of O**: Typically, oxygen has an oxidation number of -2 in compounds.
- **Let the oxidation number of Cu be X**:
- The equation for the compound is:
\[ 2X + (-2) = 0 \]
- Solving gives:
\[ 2X = 2 \implies X = +1 \]
- **Conclusion**: The oxidation number of O in Cu2O is -2, not -1. Therefore, this option is incorrect.

### Step 2: Analyze ClO3
- **Compound**: ClO3
- **Element underlined**: Cl (Chlorine)
- **Oxidation state of O**: -2
- **Let the oxidation number of Cl be Y**:
- The equation for the compound is:
\[ Y + 3(-2) = -1 \]
- Solving gives:
\[ Y - 6 = -1 \implies Y = +5 \]
- **Conclusion**: The oxidation number of Cl in ClO3 is +5, which is correct.

### Step 3: Analyze K2Cr2O7
- **Compound**: K2Cr2O7
- **Element underlined**: Cr (Chromium)
- **Oxidation state of O**: -2
- **Let the oxidation number of Cr be Z**:
- The equation for the compound is:
\[ 2(+1) + 2Z + 7(-2) = 0 \]
- Solving gives:
\[ 2 + 2Z - 14 = 0 \implies 2Z = 12 \implies Z = +6 \]
- **Conclusion**: The oxidation number of Cr in K2Cr2O7 is +6, which is correct.

### Step 4: Analyze HAuCl4
- **Compound**: HAuCl4
- **Element underlined**: Au (Gold)
- **Oxidation state of Cl**: -1
- **Let the oxidation number of Au be W**:
- The equation for the compound is:
\[ (+1) + W + 4(-1) = 0 \]
- Solving gives:
\[ 1 + W - 4 = 0 \implies W = +3 \]
- **Conclusion**: The oxidation number of Au in HAuCl4 is +3, which is correct.

### Final Conclusion:
The incorrect option among the given species is **Cu2O**, where the oxidation number of oxygen was stated as -1, but it is actually -2.

### Summary of Incorrect Options:
1. **Cu2O**: Incorrectly states O as -1 (actual is -2).
2. **ClO3**: Correctly states Cl as +5.
3. **K2Cr2O7**: Correctly states Cr as +6.
4. **HAuCl4**: Correctly states Au as +3.