Aloke, when you appear for on campus or off campus interview and when you create your CV, you update your 12th marks as whole and not specifically for Physics, Chemistry and Mathematics. So it is not mandatory to score 75% in Physics, Chemistry and Mathematics. This 75% aggregate was mandatory for appearing for JEE Advanced which is the entrance examination for admission to B.E/B.Tech in IITs. Along with IITs, 75% aggregate was also mandatory for admission to B.E/B.Tech in NITs, IIITs and CFTIs. But for this year, that 75% aggregate criteria was also removed as CBSE and ICSE have cancelled their Board exams for few subjects. So this year in specific, there is no 75% aggregate criteria. For getting placed in any company, the recruiters look at your Academic profile, your on spot answers for their questions, subject knowledge and communication skills. Your B.Tech aggregate will also help you here. So this is one area you will have to focus for the next 4 years from the time you join an Engineering College. Your ultimate goal should be to be placed with a good package which means your overall academic profile should be consistently good.