This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Folding of protein chain is due to: 
Select and explain. 
A. Amide bond, B. Hydrogen bond, C. Phosphodiesterase bond, D. Disulphide bond
B: Hydrogen bond
Answer: B: Hydrogen bond 
Explanation: Hydrophobic residues are largely buried in the protein interior, away from water and the number of hydrogen bonds and ionic interactions within protein is maximized, thus reducing the number of hydrogen bonding & ionic group that are not paired with suitable partner.
Because of favourable free energy change and cooperative bonding (i.e. one bond favours the formation of next bond), the hydrogen bonds often have an important role in the protein folding process.