Question

(A) Bond angle Cr–O–Cr in \( \text{CrO}_7^{2-} \) is 126° (B) \( \text{Na}_2\text{Cr}_2\text{O}_7 \) is used as primary standard solution in titration. (C) \( \text{K}_2\text{Cr}_2\text{O}_7 \) oxidises \( \text{Fe}^{2+} \) into \( \text{Fe}^{3+} \) in acidic medium. (D) \( \text{CrO}_4^{2-} \) and \( \text{Cr}_2\text{O}_7^{2-} \) are interconvertible by changing pH.

• A. A, C, D only
• B. B, C, D only
• C. A, B, C only
• D. A, B, D only

Answer 1

The Correct Option is A

textbf{Step 1: Analysis of Statement (A).}
In \( \text{CrO}_7^{2-} \), the bond angle Cr–O–Cr is 126°, which is a correct statement. Therefore, statement (A) is correct. Step 2: Analysis of Statement (B).
\( \text{Na}_2\text{Cr}_2\text{O}_7 \) is indeed used as a primary standard in titration, especially in redox titrations. Hence, statement (B) is correct. Step 3: Analysis of Statement (C).
\( \text{K}_2\text{Cr}_2\text{O}_7 \) is a strong oxidizing agent and oxidizes \( \text{Fe}^{2+} \) to \( \text{Fe}^{3+} \) in acidic medium, making statement (C) correct. Step 4: Analysis of Statement (D).
\( \text{CrO}_4^{2-} \) and \( \text{Cr}_2\text{O}_7^{2-} \) are interconvertible by changing the pH of the solution. This is a well-known chemical property of chromium species, making statement (D) correct. \[ \boxed{A, C, D \text{ only}} \]