Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Treatment of immunoglobulin IgG with β-mercaptoethanol gives rise to two heavy chains and two light chains peptides on SDS-PAGE.
Reason R: β-mercaptoethanol breaks peptide bond at the site of disulphide linkage.
In the light of the above statements, choose the most appropriate answer from the options given below: