Hello aspirant,

No, it is not at all hard to get 90-100 marks in JEE Advanced actually it's very easy but it depends on the difficulty level of question paper.

For scoring 90-100 marks in JEE Advanced there is no such special technique, you just need to treat it like your JEE Mains and attempt only those questions which you are sure about the answers and revise the concepts.

About the topics, for Physics, practice complete Mechanics portions with practice paper and mock tests. For Chemistry, revise thoroughly Physical Chemistry and for Mathematics, Coordinate Geometry is the game changer.

All the best