Select the correct statement:

Options

A. Be and Al show diagonal relationship
B. Be forms tetrahedral complexes `[Be(C_(2)O_(4))_(2)]^(2--)`
C. Al forms `AlF_(6)^(2-)`, an octahedral complex
D. All are correct statements

Answer

To solve the question, we need to analyze each of the provided statements regarding Beryllium and Aluminum, and determine which one is correct.

### Step-by-Step Solution:

1. **Analyze Option 1: Beryllium and Aluminum show diagonal relationship.**
- Beryllium (Be) and Aluminum (Al) do indeed show a diagonal relationship in the periodic table. This means they exhibit similar properties due to their comparable ionic radii and charge-to-radius ratios.
- **Conclusion:** This statement is true.

2. **Analyze Option 2: Beryllium forms tetrahedral complexes.**
- Beryllium typically forms tetrahedral complexes such as BeF4²⁻ and Be(C2O4)²⁻. This is a characteristic behavior of Beryllium due to its small size and high charge density.
- **Conclusion:** This statement is also true.

3. **Analyze Option 3: Aluminum forms octahedral complexes.**
- Aluminum commonly forms octahedral complexes, such as AlF6³⁻ and Al(C2O4)³⁻. The larger ionic size of Aluminum compared to Beryllium allows it to stabilize such geometries.
- **Conclusion:** This statement is true as well.

4. **Analyze Option 4: All are correct statements.**
- Since all the previous statements (1, 2, and 3) have been found to be true, this statement must also be true.
- **Conclusion:** This statement is correct.

### Final Answer:
The correct option is **Option 4: All are correct statements.**