Failed Candidates can appear for 2019-20 Board exam as a regular candidates through the School in which he/ she is studying. According to the lastest notification released by CBSE has allowed the students who have failed in class 10 or class 12 examinations from last academic year to appear as regular candidates in the upcoming board examinations.
By Proper revision and Practise
Its not possible. You need to study SST in order to pass the Board exam.
Now there are two paper in Maths 1.standard-level 2. higher-level mathematics question paper. If you are strong and confident in Maths then chose Higher Level but if you are weak then chose Standar Level.
You can check General Studies Syllabus at http://cbseacademic.nic.in/web_material/CurriculumMain20/SrSecondary/General_Studies.pdf