IISER Entrance Exam

Yes, it will be difficult.

Hi,
Please find the link below for information on the pattern and syllabus of the examination, so that you can prepare accordingly:
https://www.shiksha.com/science/iiser-entrance-exam-pattern
https://www.shiksha.com/science/iiser-entrance-exam-syllabus.

Yes, you definitely can. There are three pathways to appear in IISER exam I. e. Either through KVPY or JEE or SCB. Since you have dropped mathematics you can either go through KVPY or SCB. So, check your SCB according to your state and then you can apply if you qualify the cut-off marks.
All the best!

Yes, you are eligible for the same.

Mathematics is not a mandatory subject for the exam. However, you need to have a certain amount of marks in your board examination to appear for the test. You can apply for IISER if you have cleared your class 12th exams either this year or last year.

Yes, you can write IISER exam after completing B.Sc.

Yes, you can apply for IISER exam.