There is no Minimum fixed marks as such, all you need is thorough preparation for entrance exam.

Practising books like NCERT is must with solvibg atleast 200 questions from each chapter.The cutoff for CS shall be skyrocketed as its most demanding Specialization.

Henece, scoribg way above is the key to get through.
Solve at least 20mock exams, analyze mistakes and oractise weak areas more to save time and optimise efforts.
You can also join Coaching Institution to further mastsr the exams.