Android : exit application from fragment activity

I want to close the android application from fragment activity. Fragment layout contains two menus.one of the fragment will display the list. When we click on the list it will display the details for list in Dialog Alert that alert box contains two buttons.if you click one button it will open another activity that activity will contains list. if we click the list it will open previous activity in the fragment activity.if you click back button from this activity it is not closing the app completely.

please give me good solution to exit the app from the situation