How to mount ISO image on virtualbox

1. Open your VB
2. Select Virtual Disk
3. Now click the new Storage GUI (if you're using 3.1.0 and above)
4. The first option IDE like.. In that select Empty CD, Now right side you will find option like IDE Primary and so on left that and go to right CD drop down, there select    CD/DVD Drive and click OK.

You are done :)