Question regarding boards viva

This question is for droppers and people who have passed 12th I wanted to ask ki viva vagera me kya kya puchte hai? Like so they ask anything from the 12th syllabus or is it limited to what is coming in practical like salt analysis for chemistry and Ray optics for physics. Can you also clarify that what is asked in maths and English like please give a general idea, how can we prepare?