Assertion : In acidic medium, `K_2Cr_2O_7` exists as `Cr_2O_7^(2-)` (orange) while in basic medium it is converted to `CrO_4^(2-)` (yellow).
Reason : `K_2Cr_2O_7` is hygroscopic in nature and changes colour on reaction with water.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true and reason not is the correct explanation of assertion.
C. If assertion is trun but reason is false.
D. If both assertion and reason are false.

Explanation

To solve the question, we need to analyze the assertion and reason provided:

### Assertion:
In acidic medium, \( K_2Cr_2O_7 \) exists as \( Cr_2O_7^{2-} \) (orange) while in basic medium it is converted to \( CrO_4^{2-} \) (yellow).

### Reason:
\( K_2Cr_2O_7 \) is hygroscopic in nature and changes color on reaction with water.

### Step-by-Step Solution:

1. **Understanding the Assertion:**
- \( K_2Cr_2O_7 \) is potassium dichromate.
- In acidic conditions, the dichromate ion \( Cr_2O_7^{2-} \) is present, which is known to have an orange color.
- In basic conditions, \( Cr_2O_7^{2-} \) converts to \( CrO_4^{2-} \), which is yellow in color.
- Therefore, the assertion is true.

2. **Understanding the Reason:**
- The reason states that \( K_2Cr_2O_7 \) is hygroscopic and changes color upon reaction with water.
- While it is true that \( K_2Cr_2O_7 \) can absorb moisture from the air (hygroscopic), the color change is not primarily due to its reaction with water.
- The color change is actually due to the change in pH of the solution: acidic conditions favor the formation of \( Cr_2O_7^{2-} \) (orange), while basic conditions favor \( CrO_4^{2-} \) (yellow).
- Hence, the reason is false.

3. **Conclusion:**
- The assertion is true, and the reason is false. Therefore, the correct answer is that the assertion is correct, but the reason is incorrect.

### Final Answer:
Assertion is true; Reason is false.

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