if i select in application form obc category and i can change the my category to general in vounselling .
No, you can't change your catagory in counselling once you choose a category at the time of filling the application form. All the results, ranks and cut-offs are made accordingly as per the category you choose. Thus, you need to choose one wisely and correctly. Choose the one from which you belong. And you can't change it thereafter.
Hope you understand.
Good luck!