Question

The covalent bond length is almost the same in which of the following pairs of bonds

• A. C-H and O-H
• B. C=C and C=N
• C. C=O and N=O
• D. C-C and C-N

Hint:

Look for pairs where both atoms in the bond change by just one position in the periodic table, or where one atom is fixed and the other belongs to neighboring groups. The double bond character (\(=\)) often "tightens" the bond, making small atomic differences even less significant.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Bond length is influenced by the size of the atoms and the bond order (single, double, or triple). Pairs of bonds where the involved atoms have similar covalent radii and the same bond order will have nearly equal lengths.

Step 2: Detailed Explanation:
1. Across the second period, atomic radii are: \(C > N > O\).
2. Option C: In \(C=O\) and \(N=O\), Carbon and Nitrogen are adjacent, and Oxygen is common. Both are double bonds. Because the atomic radii of \(C\) and \(N\) are small and close to each other, the \(C=O\) (~121 pm) and \(N=O\) (~120 pm) lengths are very similar.
3. In other options, the differences are more pronounced (e.g., \(C-C\) is 154 pm while \(C-N\) is 147 pm; \(C=C\) is 134 pm while \(C=N\) is 130 pm).

Step 3: Final Answer:
The pair C=O and N=O has almost the same bond length.