About Adsense



Yes you can add an unlimited amount, but make sure none violates Adsense TOS or your entire account can be in jeopardy, not just the single website.
 
You can add as many websites as you can as long as you follow the terms of service of google adsense. It is also enough to apply just one quality website to be able to get approved in google adsense.
 
It's a good idea to make sure that ALL the sites you place ADSENSE code on are good sites that follow Google's TOS. You may also want make sure that the sites are not purpose built only to serve up adsense ads. Google feels those type of sites violate the "spirit of TOS" and they will close your account, steal the money owed to you, and never respond to your desperate pleas for just one more chance.