If you fail in one subject , then you have to first clear that subject then only you can apply for your further course. Until you haven't get your mark sheet with all subjects passed xii you won't get admission to any college whatever may be your marks in JEE main . Also you must meet the eligibility criteria of minimum 50% in PCM and 75% aggregate for nit or IIT . You will have two mark sheets. It won't affect your Jee main (b.arch.) score but it will affect your our rank in merit list during admission process in college as first attempt candidate is preferred over second attempt candidate.

Hello aspirant

If you fail in one subject of xii board, you will have to pass in that subject and meet the criteria also that is minimum 50% in PCM and 75% aggregate for NIT and IIT colleges.

It Will affect your Jee main  merit list rank also as admission to some courses is allowed only if you have passed xii in first attempt. Even if it is allowed to candidates with 2nd attempt, candidates with first attempt will be preferred .