what is the difference between alexa ranking and google ranking?/////////

IMHO..Alexa Rank and Google Rank has a different measurement, you can combine the information between these two to get a very detailed data about how your website doing on the net..Alexa for popularity and Google for info about visitor, bounce rate, and many more..

 

Google updates the PR scores in the toolbar several times a year. alexa data is very much inflated as sites move up the rankings. Don't go out and start using Alexa data to determine whether a domain is worthwhile for acquiring a link.