Hi Girish,
The following link describe the correct way to close a discussion.
Try to take a look into it.
http://scn.sap.com/community/support/blog/2013/04/03/how-to-close-a-discussion-and-why
Mark the discussion as “Answered” or assumed answered so that other members can find their answers more easily and it also shows to participants that discussion is closed.
Hope it will help you to close all your open discussions for which you have got helpful or complete information.
Regards,