Let's say I have two ads in a page. Ad 1: Big Ad 2: Small The small ad is hidden by CSS display:none. When the web browser resizes or when a mobile browser (like the iPhone) is used, the big ad gets set to display:none, and the small ad is shown. It's like they switch, thanks to CSS @media screen and (max-width: XXXpx). I wonder if this is ok, or is it allow in adsense? EDIT: Here's a live example from jsfiddle: http://jsfiddle.net/vF8eg/embedded/result/ Resize your web browser and you'll see what I mean. Note: Please disable adblock on jsfiddle to see it.
Hiding the ads can create troubles. If you are looking for responsive Adsense then you can use the code explained in this page: http://www.labnol.org/internet/google-adsense-responsive-design/25252/ That code is very easy to setup and approved by Adsense. I am using it for last one month without any problems.