Question

Statement-I : The correct increasing order of bond length among the following is $O_2^+ < O_2 < O_2^- < O_2^{2-}$.
Statement-II : The correct order of number of unpaired electrons is $O_2^{2-} < O_2^+ < O_2^- < O_2$.

• (1) Both Statement-I and Statement-II are correct
• (2) Statement-I is correct and Statement-II is incorrect
• (3) Statement-II is correct and Statement-I is incorrect
• (4) Both Statement-I and Statement-II are incorrect

Answer 1

The Correct Option is B

Molecular Orbital Theory (MOT) explains bond order, bond length, and magnetic properties (unpaired electrons).
1. Calculate Bond Order and Unpaired Electrons:
• $O_2^{+} (15e^-)$: Bond Order = 2.5, Unpaired $e^- = 1$.
• $O_2 (16e^-)$: Bond Order = 2.0, Unpaired $e^- = 2$.
• $O_2^{-} (17e^-)$: Bond Order = 1.5, Unpaired $e^- = 1$.
• $O_2^{2-} (18e^-)$: Bond Order = 1.0, Unpaired $e^- = 0$.

2. Evaluate Statement-I (Bond Length):
Bond length is inversely proportional to bond order.
Bond Order order: $O_2^{+} (2.5) > O_2 (2.0) > O_2^{-} (1.5) > O_2^{2-} (1.0)$.
Bond Length order: $O_2^{+} < O_2 < O_2^{-} < O_2^{2-}$. Statement-I is correct.

3. Evaluate Statement-II (Unpaired Electrons):
Actual counts: $O_2^{2-} (0), O_2^{+} (1), O_2^{-} (1), O_2 (2)$.
Statement-II says: $O_2^{2-} < O_2^{+} < O_2^{-} < O_2$. This implies $O_2^{+}$ has fewer unpaired electrons than $O_2^{-}$, but both have exactly 1.
Thus, the strict inequality is incorrect. Statement-II is incorrect.

Conclusion: Statement-I is correct, Statement-II is incorrect. Option (2).