Question

Which of the following statements are correct?
(A) The M³⁺/M²⁺ reduction potential for iron is greater than manganese 
(B) The higher oxidation states of first row dblock elements get stabilized by oxide ion. 
(C) Aqueous solution of Cr²⁺ can liberate hydrogen from dilute acid. 
(D) Magnetic moment of V²⁺ is observed between 4.4-5.2 BM Choose the correct answer from the options given below: 

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

Hint:

Review concepts of reduction potentials, stability of oxidation states in d-block elements, and the relationship between unpaired electrons and magnetic moment

Answer 1

The Correct Option is B

(A) Incorrect:

The reduction potential for the M³⁺/M²⁺ couple for manganese is greater than that for iron:

\[ E^\circ_{\text{Mn}^{3+}/\text{Mn}^{2+}} = +1.57 \, \text{V}, \, E^\circ_{\text{Fe}^{3+}/\text{Fe}^{2+}} = +0.77 \, \text{V} \]

Therefore, this statement is incorrect.

(B) Correct:

Higher oxidation states of first-row d-block elements are stabilized by oxide ions (O²⁻) due to the formation of strong metal-oxygen bonds. This statement is correct.

(C) Correct:

Chromium in the Cr²⁺ oxidation state can reduce H⁺ to H₂ in aqueous solution:

\[ \text{Cr}^{2+} + \text{H}^+ \rightarrow \text{Cr}^{3+} + \frac{1}{2}\text{H}_2 \]

The reduction potential \( E^\circ_{\text{Cr}^{3+}/\text{Cr}^{2+}} = -0.26 \, \text{V} \) confirms this. This statement is correct.

(D) Incorrect:

V²⁺ has three unpaired electrons, resulting in a magnetic moment of approximately 3.87 BM, which is not within the range of 4.4-5.2 BM. This statement is incorrect.

Conclusion:

• (A) Incorrect
• (B) Correct
• (C) Correct
• (D) Incorrect