if a civil engineering btech student is unable to get job in IT sector as a fresher can he/she seat in off campus placements of big IT companies which comes in IIT after giving one year drop after graduation? if he have good Coding knowledge after giving one year drop .
How much you know and the how much you can apply is the most crucial thing for any recruiter to seek from you. SO if you have good working knowledge of programming then obviously you have a high chance of getting selected in IT companies despite of being a student of Civil.
Also I would recommend you should participate in some of the internships which will give you a good working experience in the field in the one year drop which you are wiling to take.
I hope my answer helps. All the very best for your future endeavors!