Which of the following statements is incorrect?

Options

A. Mercurous ion exists as `Hg^(+)`
B. Mercurous ion is diamagnetic and exists as dimer `Hg_(2)^(2-)`
C. Mercurous ion is colourless
D. There is a metallic bond between two `Hg^(+)` ions

Answer

To determine which statement is incorrect regarding the mercurous ion (Hg2²⁺), we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding the Mercurous Ion**:
- The mercurous ion is known to exist as a dimer, specifically as Hg2²⁺, rather than as individual Hg⁺ ions. This is due to the instability of the Hg⁺ ion in the +1 oxidation state.

2. **Analyzing Option A**:
- **Statement**: "Mercurous ion exists as Hg⁺."
- **Evaluation**: This statement is incorrect. The mercurous ion does not exist as Hg⁺; it exists as Hg2²⁺. The +1 oxidation state of mercury is unstable, leading to the formation of a dimer where two Hg⁺ ions bond together.

3. **Analyzing Option B**:
- **Statement**: "Mercurous ion is diamagnetic and exists as Hg2²⁺."
- **Evaluation**: This statement is correct. The dimer Hg2²⁺ has no unpaired electrons, making it diamagnetic.

4. **Analyzing Option C**:
- **Statement**: "Mercurous ion is colorless."
- **Evaluation**: This statement is also correct. Since there are no unpaired electrons in Hg2²⁺, it does not absorb visible light and appears colorless.

5. **Analyzing Option D**:
- **Statement**: "There is a metallic bond between two Hg⁺ ions."
- **Evaluation**: This statement is correct. The bonding between the two Hg⁺ ions in the dimer Hg2²⁺ can be described as metallic bonding.

### Conclusion:
The only incorrect statement is **Option A**: "Mercurous ion exists as Hg⁺."