Which of the following covalent bonds is the longest?

• A. C–C single bond
• B. C≡C triple bond
• C. C–H bond
• D. C=C double bond

Answer: (A)

Verified step by step guidance

1. Recall that the length of a covalent bond depends on the bond order: single bonds are generally longer than double bonds, which are longer than triple bonds because more shared electron pairs pull the atoms closer together.
2. Identify the bond types given: C–C single bond (single bond), C=C double bond (double bond), C≡C triple bond (triple bond), and C–H bond (single bond between carbon and hydrogen).
3. Understand that bonds between different atoms (like C–H) can have different lengths compared to bonds between the same atoms (like C–C), so consider atomic sizes as well; hydrogen is smaller than carbon, so C–H bonds tend to be shorter than C–C single bonds.
4. Compare the bond orders and atomic sizes: the C≡C triple bond will be the shortest due to highest bond order, followed by C=C double bond, then C–C single bond, and finally C–H bond is usually shorter than C–C single bond because hydrogen is smaller.
5. Conclude that among the options, the C–C single bond is the longest because it has the lowest bond order among carbon-carbon bonds and involves two larger atoms compared to C–H.