Hi Deekshith!

the answer to you is YES!, there are two methods through which you can re-appear for board exam in order to increase your percentage. But it won't have any effect in your competitive exams as far as one is concerned about JEE MAINS OR ADVANCE but yeah there are several college which ask about 80%.

The first is the NIOS, which is National school of open schooling, where you can demand to re-appear as a private candidate with a fees charge of Rs.2000 i assume, and the practical marks would also be the same as the previous year.

the second is to appear as a private student and that too for waiting another year, and you have to give practicals again. The advantage for NIOS is you can demand to conduct the exam the exact same year.

Note- the above information is valid only from CBSE point of view as ISC doesn't conduct re-exam.

hope this answers your query, all the best

cheers!