Question

In which pair or pairs is the stronger bond found in the first species? I: \(O_2^{2-},\, O_2\)
II: \(N_2,\, N_2^+\)
III: \(NO^+,\, NO\)

• A. I only
• B. II only
• C. I and III only
• D. II and III only

Hint:

Bond order trends:
Higher bond order \(\Rightarrow\) shorter and stronger bond
Removal of antibonding electrons increases bond order
Addition of antibonding electrons decreases bond order

Answer 1

The Correct Option is D

Step 1: Bond strength is directly proportional to bond order. Higher bond order \(\Rightarrow\) stronger bond.
Step 2: Pair I: \(O_2^{2-}\) and \(O_2\) \[ \text{Bond order of } O_2 = 2 \] \[ \text{Bond order of } O_2^{2-} = 1 \] Hence, bond is stronger in \(O_2\), not in the first species. \[ \Rightarrow \text{Pair I is incorrect} \]
Step 3: Pair II: \(N_2\) and \(N_2^+\) \[ \text{Bond order of } N_2 = 3 \] \[ \text{Bond order of } N_2^+ = 2.5 \] Hence, bond is stronger in \(N_2\) (first species). \[ \Rightarrow \text{Pair II is correct} \]
Step 4: Pair III: \(NO^+\) and \(NO\) \[ \text{Bond order of } NO = 2.5 \] \[ \text{Bond order of } NO^+ = 3 \] Hence, bond is stronger in \(NO^+\) (first species). \[ \Rightarrow \text{Pair III is correct} \]
Step 5: Therefore, the stronger bond is found in the first species for pairs II and III only.