iframes in responsive sites are very problematic and it depends on how the embedded iframe is put in your site. This theme already has CSS for helping with embedded content which is based on the WordPress default theme’s own method. However, it doesn’t work on all iframes. Unfortunately, theme support does not really cover third party scripts or plugins, or custom things someone does, but what I can do for you is give you this link to check out because it will help explain some things about embedded content such as iframes: http://mobile.smashingmagazine.com/2014/02/27/making-embedded-content-work-in-responsive-design/
Also, are you using Google’s own code or are you using a plugin? If not a plugin, you may want to check out plugins that will load in your ads (but important to make sure it’s responsive as well). You can also do Google searches for responsive Google Ads.