Is it possible to set or allow users (registered) to delete thread in particular forum category and Disallow them in the others? if so how to do so?
Yes, you can make them sectional moderators.
how to do so? i have looked into it, but i m not able to give permission as required in particular categories.
If you want to only set open/close permissions:
Go to ACP > Forums & Posts {TAB} > Choose any forum's options > Moderators > You can set usergroups or some specific users as moderators.
Ofcourse you can choose permissions "there"
Ok, i have got it. It can be easily done without making moderator. Can easily select custom permission in particular forum for registered users.