Hello Bhavna pathak  ,

Marks will be awarded to everyone but only of that particular shift. It's like that if A and B both solved that question and both reached to the same answer but that answer is not given there in option. So, A just marked the answer which is nearly equal to his answer & B left that answer thinking that maybe there is some error in his calculations so better to leave the question. Now JEE committee don't know what A & B were thinking. So they will award marks to everyone. Also there are few like C who just mark the answer randomly.

you can also refer to similar questions like that of yours:

https://www.careers360.com/question-is-bonus-marks-in-jee-exam-is-given-to-all-students

GOOD LUCK with your result.