Q: As Wikipedia is a nonprofit site, and it's employees are all volunteers, where does it get the money, or in fact, does it pay to advertise on Google.com? So, does Google advertise their sites for free because they are an index of knowledge?
A: As far as I know, Wikipedia runs no ads. Are you talking about how if you search "wikipedia," you get offered a search bar right in your results page? THat's Google's doing, not Wikipedia's, and It's done for many common Web pages that work as indexes to knowledge.