Google Play itself does not pop-up ads like this (there are ads when in the Play Store app itself). Use Javier's link to try tracking down the offending app.I think it's Google Play.
That RAM Cleaner app will just fight against how Android is designed to work. The battery widget is also redundant because the battery is already listed in the notification bar. So deleting either/both of them wouldn't be a bad idea even if they don't solve the ad issue.Just by looking at your homescreen, the "Clean RAM" app and the battery app are possible culprits.
Also the "Hot Apps" looks suspicious as well.