A: `Cr_(2)O_(7)^(2-)`becomes equilibrium with `CrO_(4)^(2-)` at PH > 5
R: `Cr_(2)O_(7)^(2-)` is tetrahedral having `Cr -O- Cr angle`109º `28`

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To analyze the given assertion and reason, let's break down the problem step by step.

### Step 1: Understanding the Assertion
The assertion states that \( \text{Cr}_2\text{O}_7^{2-} \) becomes equilibrium with \( \text{CrO}_4^{2-} \) at pH > 5.

- **Explanation**: In acidic conditions (low pH), dichromate ions (\( \text{Cr}_2\text{O}_7^{2-} \)) are more prevalent. As the pH increases (becomes more basic), the equilibrium shifts towards the formation of chromate ions (\( \text{CrO}_4^{2-} \)). This is a well-known behavior in the chemistry of chromium species.

### Step 2: Understanding the Reason
The reason states that \( \text{Cr}_2\text{O}_7^{2-} \) is tetrahedral with a \( \text{Cr-O-Cr} \) angle of \( 109^\circ 28' \).

- **Explanation**: The structure of \( \text{Cr}_2\text{O}_7^{2-} \) is not tetrahedral; it is actually a distorted tetrahedral or a bipyramidal structure. The angle mentioned (\( 109^\circ 28' \)) is characteristic of a tetrahedral geometry, but the actual geometry of \( \text{Cr}_2\text{O}_7^{2-} \) is more complex due to the presence of multiple oxygen atoms and the overall molecular structure.

### Step 3: Conclusion
Based on the analysis:
- The assertion is **correct** because \( \text{Cr}_2\text{O}_7^{2-} \) does indeed convert to \( \text{CrO}_4^{2-} \) at pH > 5.
- The reason is **incorrect** because \( \text{Cr}_2\text{O}_7^{2-} \) does not have a tetrahedral structure and the angle stated is not representative of its actual geometry.

### Final Answer
Thus, the assertion (A) is true, but the reason (R) is false.

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