Proteins

Step 1: Secondary structure involves local folding like α-helix or β-sheet.

Step 1: Protein structure.
The helical structure of proteins, such as in alpha helices, is stabilized by hydrogen bonding between the backbone atoms.
Thus, the correct answer is (3).

Step 1: Understand peptide bonds.
Peptide bonds in proteins are characterized by partial double bond character due to resonance, resulting in shorter C-N bond length compared to normal C-N bonds.
Step 2: Conclusion.
The C-N bond length in proteins is smaller than usual C-N bond length. Final Answer:

Step 1: Snails use copper-based respiratory pigment.
Step 2: Haemocyanin contains copper and gives blue colour when oxygenated.