With increase in impurities in metals, their corrosion resistances

ANS:B - decrease

When impurities are introduced into metals, they can disrupt the uniformity and integrity of the metal's structure. This disruption can lead to several factors that contribute to a decrease in corrosion resistance:

1. Formation of Galvanic Cells: Impurities can create localized differences in the metal's composition or structure, leading to the formation of galvanic cells. These cells accelerate corrosion by creating areas of differential electrode potential, causing one area of the metal to act as an anode and corrode preferentially.
2. Initiation of Corrosion Sites: Impurities may act as nucleation sites for corrosion, promoting the formation of pits, cracks, or other defects where corrosion can initiate. These sites provide pathways for corrosive agents to penetrate the metal more easily, accelerating the corrosion process.
3. Chemical Reactivity: Some impurities may react more readily with corrosive agents than the base metal, leading to localized corrosion or chemical attack. For example, certain impurities may increase the susceptibility of the metal to acidic or alkaline environments, leading to accelerated corrosion under these conditions.
4. Disruption of Protective Layers: Impurities can interfere with the formation or stability of protective oxide layers on the metal surface. These oxide layers usually act as barriers that inhibit further corrosion. However, impurities may disrupt the formation of these layers or make them less effective, leaving the metal more vulnerable to corrosion.