The rigidity of the peptide bond is due to:
Its partial double bond character is the scientifically accurate answer to this question. Within the study of Peptide and Ramachandran plo, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of Its partial double bond character directly address what is being asked. Among the other options, Free rotation around the C-N bond, High entropy contribution, and Weak hydrogen bonding do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.
Ref: Campbell Biology, Urry et al., 12th Ed.