Incorrect statement regarding the structure of dichromate is 

Options

A. It has two kinds of bond lengths
B. `Cr-O-Cr` Bond angle is `126^(@)`
C. It contains `p^(pi)-d^(pi)` bonds between `Cr & O`
D. Each `'Cr'` is surrounded by 3 oxygens

Answer

To determine the incorrect statement regarding the structure of dichromate (\(Cr_2O_7^{2-}\)), we will analyze the provided statements step by step.

### Step 1: Understand the structure of dichromate
The dichromate ion (\(Cr_2O_7^{2-}\)) consists of two chromium (Cr) atoms and seven oxygen (O) atoms. The structure can be represented as follows:
- Each chromium atom is bonded to four oxygen atoms.
- The overall charge of the ion is -2.

### Step 2: Analyze the bond types and angles
1. **Bond Types**: The dichromate ion contains both sigma (\(\sigma\)) and pi (\(\pi\)) bonds. Specifically, there are p-pi and d-pi bonding interactions between the chromium and oxygen atoms.
2. **Bond Angles**: The bond angle between the chromium-oxygen bonds is approximately 126 degrees, which is a characteristic of the geometry of the dichromate ion.

### Step 3: Evaluate the statements
1. **Statement about two kinds of bond lengths**: This is true. In the dichromate ion, there are different bond lengths due to the presence of different types of bonds (single and double bonds).
2. **Statement about bond angle being 126 degrees**: This is also true. The bond angle in the dichromate ion is indeed around 126 degrees.
3. **Statement about p-pi d-pi bonding**: This is true as well. The bonding between chromium and oxygen involves p-pi and d-pi interactions.
4. **Statement about each chromium being surrounded by three oxygen atoms**: This statement is incorrect. Each chromium atom is actually surrounded by four oxygen atoms.

### Conclusion
The incorrect statement regarding the structure of dichromate is that "each chromium is surrounded by three oxygen." The correct number is four.

### Final Answer
The incorrect statement regarding the structure of dichromate is: "Each chromium is surrounded by three oxygen."

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