The inhibition efficiency afforded by Quercetin may be attributed to the presence of electron rich phenol groups and aromatic rings, while Ginkgolide A may be attributed to the presence of electron rich O. The possible reaction centers are unshared electron pair of heteroatoms and/or p-electrons of aromatic ring. Generally, Quercetin can absorb on the mild steel surface on the basis of donor–acceptor interactions between p-electrons of the O and aromatic ring and vacant d orbitals of surface iron. The schematic illustration of different modes of adsorption on metal is shown in Figure 7. Besides, the flavonoids are high reductive and can be oxidized to benzoquinone by the O2 resolved in the solution, which can inhibit the oxygen-adsorption corrosion (as shown in Figure 8)