Why are switch contacts often coated with a material?

Switch contacts are often coated with a material primarily to prevent oxidation. When switch contacts oxidize, they form a non-conductive layer on their surfaces, which can impede electrical connectivity and lead to poor performance or failure of the switch. Coatings, typically made of metals such as gold or silver, provide a barrier that protects the underlying metal from exposure to oxygen and moisture in the environment, thereby maintaining reliable conductivity and extending the lifespan of the switch.

The other choices do not accurately represent the primary purpose of contact coatings. While enhancing conductivity could be related to certain materials, it is not the main reason for coating in the context of protecting switch contacts from oxidation. Reducing friction is more relevant to mechanical components rather than electrical contacts, and decreasing weight is not a concern with switch contacts, as the integrity of the contact is far more critical than its weight.