How to turn on or off chat for a particular person in facebook:

               In facebook many of them have too many friends, this includes both known and unknown friends. When we are online in fb. We wouldn’t like to chat with some persons whether known or unknown person, at that time we can make their chat on or off

Now click on the member in the chat list who you want to make offline, then go to settings-> a list will open->in that click on the turn off chat for person. Now the member chat will turn off. If you want to make him online then go to setting->and click on turn chat for person->now the chat will turn on.