This plugin will allow you to add advertisements in the below listed spots. You can use Google adsense or any HTML ad code.
ad after menu navigation bar, just after horizontal line.
ad after question, just before answers.
ad after all answers, just before related questions.
ad after all questions.
Download Plugin (Its FREE!)
Plugin is active on http://q2a-dev.prothoughts.com
You can also use below two plugins for placing ads on your Q2A site.
https://github.com/q2amarket/q2am-simple-adverts (This plugin contains different ad spots than above)